-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Cisco Security Advisory: TCP Vulnerabilities in Multiple IOS-Based Cisco Products Revision 1.0 For Public Release 2004 April 20 21:00 UTC (GMT) - ------------------------------------------------------------------------- Summary ======= A vulnerability in the Transmission Control Protocol (TCP) specification (RFC793) has been discovered by an external researcher. The successful exploitation enables an adversary to reset any established TCP connection in a much shorter time than was previously discussed publicly. Depending on the application, the connection may get automatically re-established. In other cases, a user will have to repeat the action (for example, open a new Telnet or SSH session). Depending upon the attacked protocol, a successful attack may have additional consequences beyond terminated connection which must be considered. This attack vector is only applicable to the sessions which are terminating on a device (such as a router, switch, or computer) and not to the sessions that are only passing through the device (for example, transit traffic that is being routed by a router). In addition, this attack vector does not directly compromise data integrity or confidentiality. All Cisco products which contain TCP stack are susceptible to this vulnerability. This advisory is available at http://www.cisco.com/warp/public/707/cisco-sa-20040420-tcp-ios.shtml, and it describes this vulnerability as it applies to Cisco products that run Cisco IOS® software. A companion advisory that describes this vulnerability for products that do not run Cisco IOS software is available at http://www.cisco.com/warp/public/707/cisco-sa-20040420-tcp-nonios.shtml. Affected Products ================= Products which contain a TCP stack are susceptible to this vulnerability. All Cisco products and models are affected. The severity of the exposure depends upon the protocols and applications that utilize TCP. This attack vector is only applicable to the sessions which are terminating on a device (such as a router, switch, or computer), and not to the sessions that are only passing through the device (for example, transit traffic that is being routed by a router). Details ======= TCP is the transport layer protocol designed to provide connection-oriented reliable delivery of a data stream. To accomplish this, TCP uses a mixture of flags to indicate state and sequence numbers to identify the order in which the packets are to be reassembled. TCP also provides a number, called an acknowledgement number, that is used to indicate the sequence number of the next packet expected. The packets are reassembled by the receiving TCP implementation only if their sequence numbers fall within a range of the acknowledgement number (called a "window"). The acknowledgement number is not used in a packet with the reset (RST) flag set because a reset does not expect a packet in return. The full specification of the TCP protocol can be found at http://www.ietf.org/rfc/rfc0793.txt. According to the RFC793 specification, it is possible to reset an established TCP connection by sending a packet with the RST or synchronize (SYN) flag set. In order for this to occur, the 4-tuple must be known or guessed (source and destination IP address and ports) together with a sequence number. However, the sequence number does not have to be an exact match; it is sufficient to fall within the advertised window. This significantly decreases the effort required by an adversary: the larger the window, the easier it is to reset the connection. While source and destination IP addresses may be relatively easy to determine, the source TCP port must be guessed. The destination TCP port is usually known for all standard services (for example, 23 for Telnet, 80 for HTTP). Cisco IOS software uses predictable ephemeral ports for known services with a predictable increment (the next port which will be used for a subsequent connection). These values, while constant for a particular Cisco IOS software version and protocol, can vary from one release to another. Here is an example of a normal termination of a TCP session: Host(1) Host(2) | | | | | ACK ack=1001, window=5000 | |<----------------------------| | | Host(1) is closing the session | RST seq=1001 | |---------------------------->| | | Host(2) is closing the session In addition, the following scenario is also permitted: Host(1) Host(2) | | | | | ACK ack=1001, window=5000 | |<----------------------------| | | Host(1) is closing the session | RST seq=4321 | |---------------------------->| | | Host(2) is closing the session Note how, in the second example, the RST packet was able to terminate the session although the sequence number was not the next expected one (which is 1001). It was sufficient for the sequence number to fall within the advertised "window". In this example, Host(2) was accepting sequence numbers from 1001 to 6001 and 4321 is clearly within the acceptable range. As a general rule, all protocols where a TCP connection stays established for longer than one minute should be considered exposed. The exposure on this vulnerability can be described as follows: * Cisco IOS - All devices running Cisco IOS software are vulnerable. Only TCP sessions that are terminating on the device itself are affected since this vulnerability only affects the endpoints of a session. Sessions passing through the device are vulnerable only if the originating or receiving device is vulnerable, but they cannot be attacked on the router itself. This vulnerability does not compromise data integrity or confidentiality. It only affects availability. This vulnerability is documented in the Cisco Bug Toolkit as Bug IDs CSCed27956 ( registered customers only) and CSCed38527 ( registered customers only) . * Cisco IOS Firewall (IOS FW) - The Cisco IOS FW monitors packets passing throughout the router and maintains the session state internally. This way, it is possible to "open" required ports and allow traffic to pass and then close them after the session has finished. Since Cisco IOS FW intercepts and examines all packets passing through the device, all TCP sessions passing through the Cisco IOS FW are vulnerable to this attack. This is valid even if the originating and receiving devices themselves are not vulnerable. This vulnerability is documented in the Cisco Bug Toolkit as Bug ID CSCed93836 ( registered customers only) . * Network Address Translation (NAT) - This vulnerability does not have any effect on NAT. The NAT functionality simply rewrites ports and IP addresses. This feature does not interprete TCP flags and therefore is not vulnerable to this attack. However, the attacking packet will be passed through the router and the receiving device can be affected. Impact ====== The impact will be different for each specific protocol. While in the majority of cases a TCP connection will be automatically re-established, in some specific protocols a second order of consequences may have a larger impact than tearing down the connection itself. Border Gateway Protocol (BGP) - ----------------------------- The Cisco PSIRT has identified BGP as the protocol which has the greatest potential for impact. Both external and internal (eBGP and iBGP) sessions are equally vulnerable. If an adversary tears down a BGP session between two routers, then all routes which were advertised between these two peers will be withdrawn. This would occur immediately for the router which has been attacked and after the next update/keepalive packet is sent by the other router. The BGP peering session itself will be re-established within a minute after the attack. Depending upon the exact routing configuration, withdrawal of the routes may have any of the following consequences: * No adverse effects at all if an appropriate static route(s) has(have) been defined on both sides of the affected session. * The traffic will be rerouted along other paths. This may cause some congestion along these paths. * A portion of the network will be completely isolated and unreachable. If a BGP peering session is broken a few times within a short time interval, then BGP route dampening may be invoked. Dampening means that affected routes will be withdrawn from the Internet routing table for some period of time. By default that time is 45 minutes. During that time, all of the traffic whose route was advertised over the attacked BGP session will either be rerouted or a portion of the network will be unreachable. Route dampening is not enabled by default. Cisco IOS Firewall Feature Set - ------------------------------ It is possible to terminate an established TCP-based connection even if both endpoints are not vulnerable to this attack. Software Versions and Fixes =========================== Each row of the table describes a release train and the platforms or products for which it is intended. If a given release train is vulnerable, then the earliest possible releases that contain the fix and the anticipated date of availability for each are listed in the Rebuild, Interim, and Maintenance columns. In some cases, no rebuild of a particular release is planned; this is marked with the label "Not scheduled." A device running any release in the given train that is earlier than the release in a specific column (less than the earliest fixed release) is known to be vulnerable, and it should be upgraded at least to the indicated release or a later version (greater than the earliest fixed release label). When selecting a release, keep in mind the following definitions: * Maintenance Most heavily tested and highly recommended release of any label in a given row of the table. * Rebuild Constructed from the previous maintenance or major release in the same train, it contains the fix for a specific vulnerability. Although it receives less testing, it contains only the minimal changes necessary to effect the repair. Cisco has made available several rebuilds of mainline trains to address this vulnerability, but strongly recommends running only the latest maintenance release on mainline trains. * Interim Built at regular intervals between maintenance releases and receives less testing. Interims should be selected only if there is no other suitable release that addresses the vulnerability, and interim images should be upgraded to the next available maintenance release as soon as possible. Interim releases are not available through manufacturing, and usually they are not available for customer download from CCO without prior arrangement with the Cisco Technical Assistance Center (TAC). In all cases, customers should exercise caution to be certain the devices to be upgraded contain sufficient memory and that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, contact the Cisco TAC for assistance, as shown in the section following this table. Fixed Cisco IOS Software Images for Cisco IOS Firewall +------------+---------------------------------+ | Major | Availability of Repaired | | Release | Releases* | +------------+---------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.1-Based | | ** | | | Release | | | | +------------+---------+---------+-------------+ | 12.1 | 12.1 | | | | | (22c) | | | +------------+---------+---------+-------------+ | 12.1E | 12.1 | | | | | (19)E7 | | | | +---------+---------+-------------+ | | | | | +------------+---------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.2-Based | | ** | | | Release | | | | +------------+---------+---------+-------------+ | 12.2 | 12.2 | | | | | (21b) | | | | +---------+---------+-------------+ | | 12.2 | | | | | (23a) | | | +------------+---------+---------+-------------+ | 12.2T | 12.2 | | | | | (11)T11 | | | | +---------+---------+-------------+ | | 12.2 | | | | | (13)T12 | | | | +---------+---------+-------------+ | | 12.2 | | | | | (15)T12 | | | +------------+---------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.3-Based | | ** | | | Release | | | | +------------+---------+---------+-------------+ | 12.3 | 12.3 | | | | | (5c) | | | | +---------+---------+-------------+ | | 12.3 | | | | | (6a) | | | +------------+---------+---------+-------------+ | 12.3T | 12.3(4) | | | | | T4 | | | +------------+---------+---------+-------------+ Fixed Cisco IOS Software Releases and Migration Path +----------+-------------------------------------+ | Major | Availability of Repaired Releases* | | Release | | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 11.1 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 11.1 | 11.1 Vulnerable. Migrate to 11.2 | +----------+-------------------------------------+ | 11.1AA | 11.1AA Vulnerable. Migrate to 11.2P | +----------+-------------------------------------+ | 11.1CC | 11.1CC Vulnerable. Migrate to 12.0 | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 11.2 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 11.2 | 11.2(26f) | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | +----------+-------------+---------+-------------+ | 11.2P | 11.2(26)P6 | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | +----------+-------------+---------+-------------+ | 11.2SA | 11.2(8)SA6 Vulnerable. Migrate to | | | 12.0 | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 11.3 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 11.3 | 11.3 Vulnerable. Migrate to 12.0 | | +-------------+---------+-------------+ | | 11.3(11b)T4 | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | | +-------------+---------+-------------+ | | 11.3(11e) | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.0 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 12.0 | 12.0(28) | | | +----------+-------------+---------+-------------+ | 12.0DA | 12.0DA Vulnerable. Migrate to | | | 12.2DA | +----------+-------------------------------------+ | 12.0DB | 12.0DB Vulnerable. Migrate to | | | 12.1DB | +----------+-------------------------------------+ | 12.0DC | 12.0DC Vulnerable. Migrate to | | | 12.1DC | +----------+-------------+---------+-------------+ | 12.0S | 12.0(27)S | | | | +-------------+---------+-------------+ | | 12.0(26)S2 | | | | +-------------+---------+-------------+ | | 12.0(16)S11 | | | | +-------------+---------+-------------+ | | 12.0(24)S5 | | | | +-------------+---------+-------------+ | | 12.0(25)S3 | | | | +-------------+---------+-------------+ | | 12.0(23)S6 | | | +----------+-------------+---------+-------------+ | 12.0SL | 12.0SL Vulnerable. Migrate to 12.0 | | | (23)S3 | +----------+-------------------------------------+ | 12.0ST | 12.0ST Vulnerable. Migrate to 12.0 | | | (26)S2 | +----------+-------------------------------------+ | 12.0SX | 12.0(25)SX4 Not built - contact TAC | +----------+-------------------------------------+ | 12.0SZ | 12.0SZ Vulnerable. Migrate to 12.0 | | | (26)S2 | +----------+-------------------------------------+ | 12.0T | 12.0T Vulnerable. Migrate to 12.1 | +----------+-------------+---------+-------------+ | 12.0W5 | 12.0(28)W5 | | | | | (30) | | | +----------+-------------+---------+-------------+ | 12.0WC | 12.0(5)WC9a | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | +----------+-------------+---------+-------------+ | 12.0WT | 12.0(13)WT Vulnerable. End of | | | Engineering | +----------+-------------------------------------+ | 12.0WX | 12.0(4)WX Vulnerable. Migrate to | | | 12.0W5 | +----------+-------------------------------------+ | 12.0XA | 12.0(1)XA Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XB | 12.0(1)XB Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.0XC | 12.0(2)XC Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XD | 12.0(2)XD Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XE | 12.0(7)XE Vulnerable. Migrate to | | | 12.1E Latest | +----------+-------------------------------------+ | 12.0XG | 12.0(3)XG Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XH | 12.0(4)XH Vulnerable. Migrate to | | | 12.1 | +----------+-------------------------------------+ | 12.0XI | 12.0(4)XI Vulnerable. Migrate to | | | 12.1 | +----------+-------------------------------------+ | 12.0XJ | 12.0(4)XJ Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XK | 12.0(7)XK Vulnerable. Migrate to | | | 12.1T Latest | +----------+-------------------------------------+ | 12.0XL | 12.0(4)XL Vulnerable. Migrate to | | | 12.2 Latest | +----------+-------------------------------------+ | 12.0XM | 12.0(4)XM Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.0XN | 12.0(5)XN Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XP | 12.0(5.1)XP Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XQ | 12.0(5)XQ Vulnerable. Migrate to | | | 12.1 Latest | +----------+-------------------------------------+ | 12.0XR | 12.0(7)XR Vulnerable. Migrate to | | | 12.2 Latest | +----------+-------------------------------------+ | 12.0XS | 12.0(5)XS Vulnerable. Migrate to | | | 12.1E Latest | +----------+-------------------------------------+ | 12.0XU | 12.0(5)XU Vulnerable. Migrate to | | | 12.0(5)WC | +----------+-------------------------------------+ | 12.0XV | 12.0(7)XV Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.1 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 12.1 | 12.1(20a) | | | | +-------------+---------+-------------+ | | 12.1(4c) | | | | +-------------+---------+-------------+ | | 12.1(22a) | | | +----------+-------------+---------+-------------+ | 12.1AA | 12.1(10)AA Vulnerable. Migrate to | | | 12.2 Latest | +----------+-------------+---------+-------------+ | 12.1AX | 12.1(14)AX | | | +----------+-------------+---------+-------------+ | 12.1AY | 12.1(13)AY Vulnerable. Migrate to | | | 12.1(14)EA1 | +----------+-------------------------------------+ | 12.1DA | 12.2DA Vulnerable. Migrate to | | | 12.2DA | +----------+-------------------------------------+ | 12.1DB | 12.1(5)DB Vulnerable. Migrate to | | | 12.2B | +----------+-------------+---------+-------------+ | 12.1E | 12.1(19)E7 | | | | +-------------+---------+-------------+ | | 12.1(22)E1 | | | | +-------------+---------+-------------+ | | 12.1(11b) | | | | | E14 | | | | +-------------+---------+-------------+ | | 12.1(20)E2 Not built - contact TAC | | +-------------+---------+-------------+ | | 12.1(19)E6 | | | | +-------------+---------+-------------+ | | 12.1(13)E13 | | | | +-------------+---------+-------------+ | | 12.1(8b)E18 | | | | +-------------+---------+-------------+ | | 12.1(14)E10 | | | | +-------------+---------+-------------+ | | 12.1(13)E14 | | | +----------+-------------+---------+-------------+ | 12.1EA | 12.1(20)EA1 | | | +----------+-------------+---------+-------------+ | 12.1EB | 12.1(20)EB | | | +----------+-------------+---------+-------------+ | 12.1EC | 12.1(20)EC | | | +----------+-------------+---------+-------------+ | 12.1EO | 12.1(20)EO | | | | +-------------+---------+-------------+ | | 12.1(19)EO2 | | | | | Available | | | | | on | | | | | 2004-Apr-25 | | | +----------+-------------+---------+-------------+ | 12.1EU | 12.1(20)EU | | | +----------+-------------+---------+-------------+ | 12.1EV | 12.1(12c)EV Vulnerable. Migrate to | | | 12.2(RLS4)S | +----------+-------------+---------+-------------+ | 12.1EW | 12.1(20)EW2 | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | +----------+-------------+---------+-------------+ | 12.1EX | 12.1EX Vulnerable. Migrate to 12.1 | | | (14)E | +----------+-------------------------------------+ | 12.1EY | 12.1(10)EY Vulnerable. Migrate to | | | 12.1(14)E | +----------+-------------+---------+-------------+ | 12.1T | 12.1(5)T17 | | | +----------+-------------+---------+-------------+ | 12.1XA | 12.1(1)XA Vulnerable. Migrate to | | | 12.1(5)T18 | +----------+-------------------------------------+ | 12.1XB | 12.1(1)XB Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XC | 12.1(1)XC Vulnerable. Migrate to | | | 12.2 | +----------+-------------------------------------+ | 12.1XD | 12.1(1)XD Vulnerable. Migrate to | | | 12.2 | +----------+-------------------------------------+ | 12.1XE | 12.1(1)XE Vulnerable. Migrate to | | | 12.1E Latest | +----------+-------------------------------------+ | 12.1XF | 12.1(2)XF Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XG | 12.1(3)XG Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XH | 12.1(2a)XH Vulnerable. Migrate to | | | 12.2 | +----------+-------------------------------------+ | 12.1XI | 12.1(3a)XI Vulnerable. Migrate to | | | 12.2 Latest | +----------+-------------------------------------+ | 12.1XJ | 12.1(3)XJ Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XL | 12.1(3)XL Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.1XM | 12.1(5)XM Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.1XP | 12.1(3)XP Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XQ | 12.1(3)XQ Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.1XR | 12.1(5)XR Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.1XT | 12.1(3)XT Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1XU | 12.1(5)XU Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.1XV | 12.1(5)XV Vulnerable. Migrate to | | | 12.2XB | +----------+-------------------------------------+ | 12.1YA | 12.1(5)YA Vulnerable. Migrate to | | | 12.2(8)T | +----------+-------------------------------------+ | 12.1YB | 12.1(5)YB Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1YC | 12.1(5)YC Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.1YD | 12.1(5)YD Vulnerable. Migrate to | | | 12.2(8)T | +----------+-------------------------------------+ | 12.1YE | 12.1(5)YE5 Vulnerable. Migrate to | | | 12.2(2)YC | +----------+-------------------------------------+ | 12.1YF | 12.1(5)YF2 Vulnerable. Migrate to | | | 12.2(2)YC | +----------+-------------------------------------+ | 12.1YH | 12.1(5)YH2 Vulnerable. Migrate to | | | 12.2(13)T | +----------+-------------------------------------+ | 12.1YI | 12.1(5)YI2 Vulnerable. Migrate to | | | 12.2(2)YC | +----------+-------------------------------------+ | 12.1YJ | 12.1(11)YJ Vulnerable. Migrate to | | | 12.1EA Latest | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.2 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 12.2 | 12.2(19b) | | | | +-------------+---------+-------------+ | | 12.2(16f) | | | | +-------------+---------+-------------+ | | 12.2(21a) | | | | +-------------+---------+-------------+ | | 12.2(23) | | | | +-------------+---------+-------------+ | | 12.2(12i) | | | | +-------------+---------+-------------+ | | 12.2(10g) | | | | +-------------+---------+-------------+ | | 12.2(13e) | | | | +-------------+---------+-------------+ | | 12.2(17d) | | | | +-------------+---------+-------------+ | | 12.2(21b) | | | | +-------------+---------+-------------+ | | 12.2(23a) | | | +----------+-------------+---------+-------------+ | 12.2B | 12.2(2)B - 12.2(4)B7 Vulnerable. | | | Migrate to 12.2(13)T12 | | +-------------------------------------+ | | 12.2(4)B8 AND FWD Vulnerable. | | | Migrate to 12.3(5a)B1 | +----------+-------------+---------+-------------+ | 12.2BC | 12.2(15) | | | | | BC1C | | | +----------+-------------+---------+-------------+ | 12.2BW | 12.2(4)BW Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------+---------+-------------+ | 12.2BX | 12.2(16)BX2 | | | +----------+-------------+---------+-------------+ | 12.2BY | 12.2(4)BY Vulnerable. Migrate to | | | 12.2(15)B | | +-------------------------------------+ | | 12.2(8)BY Vulnerable. Migrate to | | | 12.2(8)ZB | | +-------------------------------------+ | | 12.2(2)BY Vulnerable. Migrate to | | | 12.2(8)BZ | +----------+-------------------------------------+ | 12.2BZ | 12.2(15)BZ Vulnerable. Migrate to | | | 12.2(16)BX | +----------+-------------------------------------+ | 12.2CX | 12.2(11)CX Vulnerable. Migrate to | | | 12.2(15)BC | +----------+-------------------------------------+ | 12.2CY | 12.2(11)CY Vulnerable. Migrate to | | | 12.2(13)BC1C | +----------+-------------------------------------+ | 12.2DD | 12.2DD Vulnerable. Migrate to 12.2 | | | (4)B1 | +----------+-------------------------------------+ | 12.2DX | 12.2(1)DX Vulnerable. Migrate to | | | 12.2DD | | +-------------------------------------+ | | 12.2(2)DX Vulnerable. Migrate to | | | 12.2B Latest | +----------+-------------+---------+-------------+ | 12.2EW | 12.2(18)EW | | | +----------+-------------+---------+-------------+ | 12.2JA | 12.2(13)JA4 | | | | +-------------+---------+-------------+ | | 12.2(13)JA2 | | | | +-------------+---------+-------------+ | | 12.2(11)JA3 | | | +----------+-------------+---------+-------------+ | 12.2MC | 12.2(15) | | | | | MC1B | | | +----------+-------------+---------+-------------+ | 12.2S | 12.2(22)S | | | | +-------------+---------+-------------+ | | 12.2(14)S7 | | | | +-------------+---------+-------------+ | | 12.2(20)S1 | | | | +-------------+---------+-------------+ | | 12.2(20)S3 | | | | | Available | | | | | on | | | | | 2004-Apr-21 | | | | +-------------+---------+-------------+ | | 12.2(18)S3 | | | +----------+-------------+---------+-------------+ | 12.2SE | 12.2(18)SE | | | +----------+-------------+---------+-------------+ | 12.2SW | 12.2(21)SW | | | +----------+-------------+---------+-------------+ | 12.2SX | 12.2(17a) | | | | | SX2 | | | +----------+-------------+---------+-------------+ | 12.2SXA | 12.2(17b) | | | | | SXA1 | | | +----------+-------------+---------+-------------+ | 12.2SXB | 12.2(17d)SXB1 Not built - contact | | | TAC | +----------+-------------+---------+-------------+ | 12.2SY | 12.2(14)SY3 | | | +----------+-------------+---------+-------------+ | 12.2SZ | 12.2(14)SZ6 | | | +----------+-------------+---------+-------------+ | 12.2T | 12.2(15)T11 | | | | +-------------+---------+-------------+ | | 12.2(13)T12 | | | | +-------------+---------+-------------+ | | 12.2(11)T11 Not built - contact TAC | | +-------------+---------+-------------+ | | 12.2(13)T11 | | | +----------+-------------+---------+-------------+ | 12.2XA | 12.2(2)XA Vulnerable. Migrate to | | | 12.2(11)T | +----------+-------------------------------------+ | 12.2XB | 12.2(2)XB Vulnerable. Migrate to | | | 12.2(15)T | +----------+-------------------------------------+ | 12.2XC | 12.2(2)XC Vulnerable. Migrate to | | | 12.2(8)ZB | +----------+-------------------------------------+ | 12.2XD | 12.2(1)XD Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XE | 12.2(1)XE Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XF | 12.2(1)XF1 Vulnerable. Migrate to | | | 12.2(4)BC1C | +----------+-------------------------------------+ | 12.2XG | 12.2(2)XG Vulnerable. Migrate to | | | 12.2(8)T | +----------+-------------------------------------+ | 12.2XH | 12.2(2)XH Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XI | 12.2(2)XI2 Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XJ | 12.2(2)XJ Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XK | 12.2(2)XK Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XL | 12.2(4)XL Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XM | 12.2(4)XM Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XN | 12.2(2)XN Vulnerable. Migrate to | | | 12.2(11)T | +----------+-------------------------------------+ | 12.2XQ | 12.2(2)XQ Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XS | 12.2(1)XS Vulnerable. Migrate to | | | 12.2(11)T | +----------+-------------------------------------+ | 12.2XT | 12.2(2)XT Vulnerable. Migrate to | | | 12.2(11)T | +----------+-------------------------------------+ | 12.2XU | 12.2(2)XU Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2XW | 12.2(4)XW Vulnerable. Migrate to | | | 12.2(13)T12 | +----------+-------------------------------------+ | 12.2YA | 12.2(4)YA Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2YB | 12.2(4)YB Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2YC | 12.2(2)YC Vulnerable. Migrate to | | | 12.2(11)T11 | +----------+-------------------------------------+ | 12.2YD | 12.2(8)YD Vulnerable. Migrate to | | | 12.2(8)YY | +----------+-------------------------------------+ | 12.2YE | 12.2(9)YE Vulnerable. Migrate to | | | 12.2S | +----------+-------------------------------------+ | 12.2YF | 12.2(4)YF Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2YG | 12.2(4)YG Vulnerable. Migrate to | | | 12.2(13)T12 | +----------+-------------------------------------+ | 12.2YH | 12.2(4)YH Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2YJ | 12.2(8)YJ Vulnerable. Migrate to | | | 12.2(15)T12 | +----------+-------------------------------------+ | 12.2YK | 12.2(2)YK Vulnerable. Migrate to | | | 12.2(13)ZC | +----------+-------------------------------------+ | 12.2YL | 12.2(8)YL Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YM | 12.2(8)YM Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YN | 12.2(8)YN Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YO | 12.2(9)YO Vulnerable. Migrate to | | | 12.2(14)SY | +----------+-------------------------------------+ | 12.2YP | 12.2(11)YP Vulnerable. Migrate to | | | 12.2T Latest | +----------+-------------------------------------+ | 12.2YQ | 12.2(11)YQ Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YR | 12.2(11)YR Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YS | 12.2(11)YS Vulnerable. Migrate to | | | 12.3T | +----------+-------------------------------------+ | 12.2YT | 12.2(11)YT Vulnerable. Migrate to | | | 12.2(15)T | +----------+-------------------------------------+ | 12.2YU | 12.2(11)YU Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YV | 12.2(11)YV Vulnerable. Migrate to | | | 12.3(4)T | +----------+-------------------------------------+ | 12.2YW | 12.2(8)YW Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------------------------------+ | 12.2YX | 12.2(11)YX Vulnerable. Migrate to | | | 12.2(RLS3)S | +----------+-------------------------------------+ | 12.2YY | 12.2(8)YY Vulnerable. Migrate to | | | 12.3(1)T | +----------+-------------------------------------+ | 12.2YZ | 12.2(11)YZ Vulnerable. Migrate to | | | 12.2(14)SZ | +----------+-------------+---------+-------------+ | 12.2ZA | 12.2(14)ZA6 | | | +----------+-------------+---------+-------------+ | 12.2ZB | 12.2(8)ZB Vulnerable. Migrate to | | | 12.3T | +----------+-------------------------------------+ | 12.2ZC | 12.2(13)ZC Vulnerable. Migrate to | | | 12.3T | +----------+-------------+---------+-------------+ | 12.2ZD | 12.2(13)ZD1 | | | +----------+-------------+---------+-------------+ | 12.2ZE | 12.2(13)ZE Vulnerable. Migrate to | | | 12.3 | +----------+-------------------------------------+ | 12.2ZF | 12.2(13)ZF Vulnerable. Migrate to | | | 12.3(4)T | +----------+-------------------------------------+ | 12.2ZG | 12.2(13)ZG Vulnerable. Migrate to | | | 12.3(4)T | +----------+-------------------------------------+ | 12.2ZH | 12.2(13)ZH Vulnerable. Migrate to | | | 12.3(4)T | +----------+-------------------------------------+ | 12.2ZI | 12.2(11)ZI Vulnerable. Migrate to | | | 12.2(18)S | +----------+-------------+---------+-------------+ | 12.2ZJ | 12.2(15)ZJ5 | | | | +-------------+---------+-------------+ | | 12.2(15)ZJ4 | | | +----------+-------------+---------+-------------+ | 12.2ZK | 12.2(15)ZK Vulnerable. Migrate to | | | 12.3T | +----------+-------------------------------------+ | 12.2ZL | 12.2(15)ZL Vulnerable. Migrate to | | | 12.3(7)T | +----------+-------------------------------------+ | 12.2ZN | 12.2(15)ZN Vulnerable. Migrate to | | | 12.3(2)T | +----------+-------------+---------+-------------+ | 12.2ZP | 12.2(13)ZP3 | | | +----------+-------------+---------+-------------+ | Affected | Rebuild | Interim | Maintenance | | 12.3 | | ** | | | -Based | | | | | Release | | | | +----------+-------------+---------+-------------+ | 12.3 | 12.3(3e) | | | | +-------------+---------+-------------+ | | 12.3(6) | | | | +-------------+---------+-------------+ | | 12.3(5b) | | | +----------+-------------+---------+-------------+ | 12.3B | 12.3(5a)B | | | | +-------------+---------+-------------+ | | 12.3(3)B1 | | | +----------+-------------+---------+-------------+ | 12.3BW | 12.3(1a)BW Vulnerable. Migrate to | | | 12.3B | +----------+-------------+---------+-------------+ | 12.3T | 12.3(2)T4 | | | | +-------------+---------+-------------+ | | 12.3(7)T1 Not built - contact TAC | | +-------------+---------+-------------+ | | 12.3(4)T3 | | | +----------+-------------+---------+-------------+ | 12.3XA | 12.3(2)XA Vulnerable. Contact TAC. | +----------+-------------+---------+-------------+ | 12.3XB | 12.3(2)XB2 | | | +----------+-------------+---------+-------------+ | 12.3XC | 12.3(2)XC2 | | | +----------+-------------+---------+-------------+ | 12.3XD | 12.3(4)XD1 | | | +----------+-------------+---------+-------------+ | 12.3XE | 12.3(2)XE Vulnerable. Migrate to | | | 12.3T | +----------+-------------------------------------+ | 12.3XF | 12.3(2)XF Vulnerable. Contact TAC | | | if needed. | +----------+-------------+---------+-------------+ | 12.3XG | 12.3(4)XG | | | +----------+-------------+---------+-------------+ | 12.3XH | 12.3(4)XH | | | +----------+-------------+---------+-------------+ | 12.3XI | 12.3(7)XI Vulnerable. Migrate to | | | 12.3T | +----------+-------------------------------------+ | 12.3XJ | 12.3(7)XJ Vulnerable. Contact TAC | | | if needed | +----------+-------------+---------+-------------+ | 12.3XK | 12.3(4)XK | | | +----------+-------------+---------+-------------+ | 12.3XL | 12.3(7)XL Vulnerable. Contact Tac | | | if needed | +----------+-------------------------------------+ | 12.3XM | 12.3(9)XM Vulnerable. Contact TAC | | | if needed. | +----------+-------------------------------------+ | 12.3XN | 12.3(4)XN Vulnerable. Contact TAC | | | if needed. | +----------+-------------------------------------+ | 12.3XQ | 12.3(4)XQ Vulnerable. Contact TAC | | | if needed. | +----------+-------------------------------------+ | * All dates are estimated and subject to | | change. | | | | ** Interim releases are subjected to less | | rigorous testing than regular maintenance | | releases, and may have serious bugs. | +------------------------------------------------+ Obtaining Fixed Software ======================== Customers with Service Contracts Customers with contracts should obtain upgraded software through their regular update channels. For most customers, this means that upgrades should be obtained through the Software Center on Cisco's worldwide website at http://www.cisco.com. Customers using Third-party Support Organizations Customers whose Cisco products are provided or maintained through prior or existing agreement with third-party support organizations such as Cisco Partners, authorized resellers, or service providers should contact that support organization for assistance with the upgrade, which should be free of charge. Customers without Service Contracts Customers who purchase direct from Cisco but who do not hold a Cisco service contract and customers who purchase through third-party vendors but are unsuccessful at obtaining fixed software through their point of sale should get their upgrades by contacting the Cisco Technical Assistance Center (TAC). TAC contacts are as follows. * +1 800 553 2447 (toll free from within North America) * +1 408 526 7209 (toll call from anywhere in the world) * e-mail: tac@cisco.com See http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml for additional TAC contact information, including special localized telephone numbers and instructions and e-mail addresses for use in various languages. Please have your product serial number available and give the URL of this notice as evidence of your entitlement to a free upgrade. Free upgrades for non-contract customers must be requested through the TAC. Please do not contact either "psirt@cisco.com" or "security-alert@cisco.com" for software upgrades. Workarounds =========== The effectiveness of any workaround is dependent on specific customer situations such as product mix, network topology, traffic behavior, and organizational mission. Due to the variety of affected products and releases, customers should consult with their service provider or support organization to ensure any applied workaround is the most appropriate for use in the intended network before it is deployed. There are no workarounds available to mitigate the effects of this vulnerability on Cisco IOS Firewall. For BGP, we will present the workaround and only a few mitigation techniques. For additional information regarding BGP security risk assessment, mitigation techniques, and deployment best practices, please consult ftp://ftp-eng.cisco.com/cons/isp/security/ BGP-Risk-Assesment-v.pdf. * BGP MD5 secret The workaround for BGP is to configure MD5 secret for each session between peers. This can be configured as shown in the following example: router(config)#router bgp <AS-_number> router(config-router)#neighbor <IP_address> password <enter_your_secret_here> It is necessary to configure the same shared MD5 secret on both peers and at the same time. Failure to do so will break the existing BGP session and the new session will not get established until the exact same secret is configured on both devices. For a detailed discussion on how to configure BGP, refer to the following document http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/ products_configuration_guide_chapter09186a00800ca571.html . Once the secret is configured, it is prudent to change it periodically. The exact period must fit within your company security policy but it should not be longer than a few months. When changing the secret, again it must be done at the same time on both devices. Failure to do so will break your existing BGP session. The exception is if your Cisco IOS software release contains the integrated CSCdx23494 ( registered customers only) fix. With this fix, the BGP session will not be terminated when the MD5 secret is changed only on one side. The BGP updates, however, will not be processed until either the same secret is configured on both devices or the secret is removed from both devices. It is possible to mitigate the exposure for BGP on this vulnerability by applying one or more of the following measures which will lessen the potential for the necessary spoofing required to implement a successful attack: * Blocking access to the core infrastructure Although it is often difficult to block traffic transiting your network, it is possible to identify traffic which should never be allowed to target your infrastructure devices and block that traffic at the border of your network. Infrastructure access control lists (ACLs) are considered a network security best practice and should be considered as a long-term addition to good network security as well as a workaround for this specific vulnerability. The white paper entitled "Protecting Your Core: Infrastructure Protection Access Control Lists", available at http://www.cisco.com/warp/public/707/ iacl.html, presents guidelines and recommended deployment techniques for infrastructure protection ACLs. Exceptions would include any devices which have a legitimate reason to access your infrastructure (for example, BGP peers, NTP sources, DNS serves, and so on). All other traffic must be able to traverse your network without terminating on any of your devices. * Configure anti-spoofing measures on the network edge In order for an adversary to use the attack vector described in this advisory, it must send packets with the source IP address equal to one of the BGP peers. You can block spoofed packets either using the Unicast Reverse Path Forwarding (uRPF) feature or by using access control lists (ACLs). By enabling uRPF, all spoofed packets will be dropped at the first device. To enable uRPF, use the following commands: router(config)#ip cef router(config)#ip verify unicast reverse-path Please consult http://www.cisco.com/en/US/products/sw/iosswrel/ps1835 /products_configuration_guide_chapter09186a00800ca7d4.html and ftp:// ftp-eng.cisco.com/cons/isp/security/URPF-ISP.pdf for further details on how uRPF works and how to configure it in various scenarios. This is especially important if you are using asymmetric routing. ACLs should also be deployed as close to the edge as possible. Unlike uRPF, you must specify the exact IP range that is permitted. Specifying which addresses should be blocked is not the optimal solution because it tends to be harder to maintain. Caution: In order for anti-spoofing measures to be effective, they must be deployed at least one hop away from the devices which are being protected. Ideally, they will be deployed at the network edge facing your customers. * Packet rate limiting RST packets are rate-limited in Cisco IOS software by default. This feature is introduced in Cisco IOS Software Release 10.2. In the case of a storm of RST packets, they are effectively limited to one packet per second. In order to be successful, an attacker must terminate connection with the first few packets. Otherwise, the attack is deemed to be impracticably long. On the other hand, SYN packets are not rate-limited in any way. Rate limiting can be accomplished either by using Committed Access Rate (CAR) or by Control Plane Policing (CPP). While CPP is the recommended approach, it is available only for Cisco IOS Software Releases 12.2(18)S and 12.3(4)T. It is currently supported only on the following routers: 1751, 2600/2600-XM, 3700, 7200, and 7500 Series. CAR can be configured as follows: router(config)#access-list 103 deny tcp any host 10.1.1.1 established router(config)#access-list 103 permit tcp any host 10.0.0.1 router(config)#interface <interface> <interface #> router(config-if)#rate-limit input access-group 103 8000 8000 8000 conform-action transmit exceed-action drop For details on how to configure and deploy CPP, please consult the following document http://www.cisco.com/en/US/products/sw/iosswrel/ ps1838/products_white_paper09186a0080211f39.shtml Exploitation and Public Announcements ===================================== The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability described in this advisory. The exploitation of the vulnerability with packets having RST flag set (reset packets) was discovered by Paul (Tony) Watson of OSVDB.org. The extension of the attack vector to packets with SYN flag was discovered by the vendors cooperating on the resolution of this issue. Status of This Notice: INTERIM ============================== This is a INTERIM advisory. Although Cisco cannot guarantee the accuracy of all statements in this advisory, all of the facts have been checked to the best of our ability. Cisco does not anticipate issuing updated versions of this advisory unless there is some material change in the facts. Should there be a significant change in the facts, Cisco may update this advisory. A stand-alone copy or Paraphrase of the text of this Security Advisory that omits the distribution URL in the following section is an uncontrolled copy, and may lack important information or contain factual errors. Distribution ============ This advisory will be posted on Cisco's worldwide website at http://www.cisco.com/warp/public/707/cisco-sa-20040420-tcp-ios.shtml. In addition to worldwide web posting, a text version of this notice is clear-signed with the Cisco PSIRT PGP key and is posted to the following e-mail and Usenet news recipients. * cust-security-announce@cisco.com * first-teams@first.org (includes CERT/CC) * bugtraq@securityfocus.com * vulnwatch@wulnwatch.org * cisco@spot.colorado.edu * cisco-nsp@puck.nether.net * full-disclosure@lists.netsys.com * comp.dcom.sys.cisco@newsgate.cisco.com Future updates of this advisory, if any, will be placed on Cisco's worldwide website, but may or may not be actively announced on mailing lists or newsgroups. Users concerned about this problem are encouraged to check the above URL for any updates. Revision History ================ +----------+-------------+----------------+ | Revision | 2004-Apr-20 | Initial public | | 1.0 | | release. | +----------+-------------+----------------+ Cisco Security Procedures ========================= Complete information on reporting security vulnerabilities in Cisco products, obtaining assistance with security incidents, and registering to receive security information from Cisco, is available on Cisco's worldwide website at http://www.cisco.com/warp/public/707/ sec_incident_response.shtml. This includes instructions for press inquiries regarding Cisco Security Notices. All Cisco Security Advisories are available at http://www.cisco.com/go/psirt. - ------------------------------------------------------------------------- All contents are Copyright © 1992-2004 Cisco Systems, Inc. All rights reserved. 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