Clamav 0.65 DoS vulnerability

[pahud]

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Gentoo Linux Security Advisory GLSA 200402-07
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~ http://security.gentoo.org
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~ Severity: Normal
~ Title: Clamav 0.65 DoS vulnerability
~ Date: February 11, 2004
~ Bugs: #41248
~ ID: 200402-07

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Synopsis
========

Oliver Eikemeier has reported a vulnerability in clamav, which can be
exploited by a malformed uuencoded message causing a denial of service
for programs that rely on the clamav daemon, such as SMTP daemons.

Background
==========

Clam AntiVirus is a GPLed anti-virus toolkit, designed for integration
with mail servers to perform attachment scanning. Clam AV also provides
a command line scanner and a tool for fetching updates of the virus
database.

Description
===========

Oliver Eikemeier of Fillmore Labs discovered the overflow in Clam AV
0.65 when it handled malformed UUEncoded messages, causing the daemon to
shut down.

The problem originated in libclamav which calculates the line length of
an uuencoded message by taking the ASCII value of the first character
minus 64 while doing an assertion if the length is not in the allowed
range, effectively terminating the calling program as clamav would not
be available.

Impact
======

A malformed message such as the one below would cause a denial of
service, and depending on the server configuration this may impact other
daemons relying on Clam AV in a fatal manner.

To exploit the vulnerability, you can add the following [ excluding the
two lines ] to ~/clamtest.mbox:

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~From -

begin 644 byebye
byebye
end
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Then do "clamscan --mbox -v ~/clamtest.mbox" or "clamdscan -v
~/clamtest.mbox; ps ax | grep clam": the former will cause an assertion
and a segmentation fault, the latter would cause the daemon to shut down.

Workaround
==========

There is no immediate workaround, a software upgrade is required.

Resolution
==========

All users are urged to upgrade their Clam AV installations to Clam AV 0.67:

~ # emerge sync
~ # emerge -pv ">=net-mail/clamav-0.6.7"
~ # emerge ">=net-mail/clamav-0.6.7"

Concerns?
=========

Security is a primary focus of Gentoo Linux and ensuring the
confidentiality and security of our users machines is of utmost
importance to us. Any security concerns should be addressed to
security@gentoo.org or alternatively, you may file a bug at
http://bugs.gentoo.org.

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