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Squid Proxy Cache Security Update Advisory SQUID-2008:1
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Advisory ID: SQUID-2008:1
Date: June 22, 2008
Summary: Remote denial of service in SNMP parser
Affected versions: All 3.0 versions up to 3.0.STABLE7
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http://www.squid-cache.org/Advisories/SQUID-2004_3.txt
http://www.squid-cache.org/Advisories/SQUID-2008_1.txt
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0918
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Problem Description:
Advisory 2004-3 was fixed in 2.5.STABLE7 and all later 2.x releases,
but was unfortunately not duplicated in the 3.x branch.
A bug exists in the ASN1 parser used in Squid's SNMP library. This
code fails to fully validate certain fields in SNMP queries. A
specially-crafted message may contain negative values, which Squid
passes to the malloc() function. This may lead to a segmentation
violation and cause Squid to restart.
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Severity:
The bug is significant because it forces squid to restart, thus
disrupting active transactions. The buggy code is executed even
before Squid makes any access control checks (i.e. snmp_access).
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Updated Packages:
The Squid-3.0.STABLE7 release contains a fix for this
problem. You can download the Squid-3.0.STABLE7 release from
ftp://ftp.squid-cache.org/pub/squid-3/STABLE/
http://www.squid-cache.org/Versions/v3/3.0/
or the mirrors (may take a while before all mirrors are updated).
For a list of mirror sites see
http://www.squid-cache.org/Mirrors/ftp-mirrors.html
http://www.squid-cache.org/Mirrors/http-mirrors.html
An individual patch for this issues can be found in our
patch archive for version Squid-3.0.STABLE6:
http://www.squid-cache.org/Versions/v3/3.0/changesets/b8826.patch
If necessary, this short patch should also apply to any version
of Squid 3.0 released before June 2008.
If you are using a prepackaged version of Squid then please
refer to the package vendor for availability information on
updated packages.
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Determining if your version is vulnerable:
This bug is present by default in all 3.0 releases before
3.0.STABLE7 since SNMP support is present by default.
However, Squid is vulnerable only if it is listening for SNMP
queries on a UDP port. The default configuration in 3.0 is for
the SNMP port to be closed.
Squid is at risk unless built with configure option --disable-snmp.
You can check if squid.conf contains the 'snmp_port' option with
a non-zero value.
Or if Squid's cache.log file contains the following message:
Accepting SNMP messages on port 3401, FD nn.
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Workarounds:
The best workaround is to close Squid's SNMP port, at least
temporarily. Close SNMP port by removing the snmp_port directive
or setting it to '0'.
Note that in 3.0 releases the default SNMP port setting is closed.
This differs form the original 2004-3 advisory.
If your SNMP agent runs on the same host as Squid, use the loopback
IP address and use a packet filter rule to block SNMP messages
from outside hosts. You can bind Squid's SNMP port to the loopback
address with this directive:
snmp_incoming_address 127.0.0.1
Restart or reconfigure Squid after editing squid.conf.
If your SNMP agent runs on a different host as Squid, configure
the firewall on your Squid box to only permit SNMP traffic between
your trusted agent and the Squid SNMP port.
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Contact details for the Squid project:
For installation / upgrade support: Your first point of contact
should be your binary package vendor.
If your install is built from the original Squid sources, then
the squid-users@xxxxxxxxxxxxxxx mailing list is your primary
support point. (see <http://www.squid-cache.org/mailing-lists.html>
for subscription details).
For bug reporting, particularly security related bugs the
squid-bugs@xxxxxxxxxxxxxxx mailing list is the appropriate forum.
It's a closed list (though anyone can post) and security related
bug reports are treated in confidence until the impact has been
established. For non security related bugs, the squid bugzilla
database should be used <http://www.squid-cache.org/bugs/>.
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Credits:
The vulnerability was reported by iDEFENSE Labs (www.idefense.com).
Henrik Nordstrom developed the patch for snmplib/asn1.c
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Revision history:
2004-10-05 00:00 GMT Disclosure of vulnerability by iDEFENSE
2004-10-25 02:10 GMT Initial release of 2004-3 document
2008-06-26 01:28 GMT Revision for Squid 3.0 regression
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