-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
National Cyber Alert System
Technical Cyber Security Alert TA08-162A
SNMPv3 Authentication Bypass Vulnerability
Original release date: June 10, 2008
Last revised: --
Source: US-CERT
Systems Affected
* Multiple Implementations of SNMPv3
Overview
A vulnerability in the way implementations of SNMPv3 handle specially
crafted packets may allow authentication bypass.
I. Description
The Simple Network Management Protocol (SNMP) is a widely deployed
protocol that is commonly used to monitor and manage network devices.
SNMPv3 ( RFC 3410) supports a user-based security model (RFC 3414)
that incorporates security features such as authentication and privacy
control. Authentication for SNMPv3 is done using keyed-hash message
authentication code (HMAC), a message authentication code calculated
using a cryptographic hash function in combination with a secret key.
Implementations of SNMPv3 may allow a shortened HMAC code in the
authenticator field to authenticate to an agent or a trap daemon using
a minimum HMAC of one byte. Reducing the HMAC to one-byte HMAC makes
brute-force authentication trivial. This issue is known to affect
Net-SNMP and UCD-SNMP. Other SNMP implementations may also be
affected.
II. Impact
This vulnerability allows attackers to read and modify any SNMP object
that can be accessed using the authentication credentials that got
them into the system. Attackers exploiting this vulnerability can view
and modify the configuration of these devices. Attackers must gain
access using credentials with write privileges in order to modify
configurations.
III. Solution
Upgrade
Please consult your vendor for more information.
Apply a patch
Net-SNMP has released a patch to address this issue. For more
information, refer to SECURITY RELEASE: Multiple Net-SNMP Versions
Released. Users are encouraged to apply the patch as soon as possible.
Note that patch should apply cleanly to UCD-snmp too.
Enable the SNMPv3 privacy subsystem
The configuration should be modified to enable the SNMPv3 privacy
subsystem to encrypt the SNMPv3 traffic using a secret, private key.
This option does not encrypt the HMAC, but does minimize the possible
affects from this vulnerability.
IV. References
* RFC 3410 - <http://tools.ietf.org/html/rfc3410>
* RFC 3414 - <http://tools.ietf.org/html/rfc3414>
* SECURITY RELEASE: Multiple Net-SNMP Versions Released -
<http://sourceforge.net/forum/forum.php?forum_id=833770 >
* US-CERT Vulnerability Note -
<http://www.kb.cert.org/vuls/id/878044>
____________________________________________________________________
The most recent version of this document can be found at:
<http://www.us-cert.gov/cas/techalerts/TA08-162A.html>
____________________________________________________________________
Feedback can be directed to US-CERT Technical Staff. Please send
email to <cert@xxxxxxxx> with "TA08-162A Feedback VU#878044" in the
subject.
____________________________________________________________________
For instructions on subscribing to or unsubscribing from this
mailing list, visit <http://www.us-cert.gov/cas/signup.html>.
____________________________________________________________________
Produced 2008 by US-CERT, a government organization.
Terms of use:
<http://www.us-cert.gov/legal.html>
____________________________________________________________________
Revision History
June 10 2008: Initial release
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.2.1 (GNU/Linux)
iQEVAwUBSE6Wv3IHljM+H4irAQI5GQgAm31aOF6lk2Gsur4fcrG5US7bIFpo8ydi
5zhopMQAabueJkHlRk8yOAHjtT/oTTIATTqhHIOStIAenR1XJ7GDA0YS2MBMu34Y
9tSH0uValQsOxAscalR9sCwPbdKQRScp+KTW9/W1qwadsqrJ2fe6J4Mh1zePWONg
EPmj0ZzLDDiAA6kaBq90Pcwfl8sS8muSwatyF68CVlX2A8i87rvn/bH8efwWT0ps
dDcyba7NMbVJ2TgtJ99a7cL9AwKrZZqptnc8aAqjXQwi9H9LsS/k5MMIMvffkqc3
TA3Igt9DjuCbkYvPCaTyJrNZKvFj92h9nVD7cL8f3Ofu888rakJI0A==
=yTkQ
-----END PGP SIGNATURE-----
