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Category:   Application (Security)  >   Clam AntiVirus Vendors:   clamav.sourceforge.net
(Gentoo Issues Fix) Clam AntiVirus UUDecode Flaw Lets Remote Users Crash 'clamd'
SecurityTracker Alert ID:  1009104
SecurityTracker URL:  http://securitytracker.com/id/1009104
CVE Reference:   GENERIC-MAP-NOMATCH   (Links to External Site)
Date:  Feb 18 2004
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 0.65 and prior versions
Description:   A vulnerability was reported in Clam AntiVirus. A remote user can cause 'clamd' to crash.

It is reported that a remote user can send an e-mail message containing a uuencoded line with an illegal line length value (such as a alphabetic character) via an e-mail system that uses 'clamd' to trigger a uudecoding vulnerability. According to the report, libclamav will calculate the length based on the ASCII value of the first character minus 64. If the resulting value is not within the proper range, the software will issue an assert() call to terminate the calling program, the report said.

To demonstration, the report indicates that you can save the following text to the '~/clamtest.mbox' file (being sure to remove the leading 'X' character):

XFrom -
X
Xbegin 644 byebye
Xbyebye
Xend

Then, you can run the following command to trigger the flaw:

# clamscan --mbox -v ~/clamtest.mbox

Impact:   A remote user can cause 'clamd' and applications that rely upon the daemon to crash.
Solution:   Gentoo has released a fix and recommends that all users 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"

Vendor URL:  www.clamav.net/ (Links to External Site)
Cause:   Exception handling error
Underlying OS:  Linux (Gentoo)

Message History:   This archive entry is a follow-up to the message listed below.
Feb 10 2004 Clam AntiVirus UUDecode Flaw Lets Remote Users Crash 'clamd'



 Source Message Contents

Subject:  [gentoo-announce] [ GLSA 200402-07 ] Clamav 0.65 DoS vulnerability


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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:

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
~From -

begin 644 byebye
byebye
end
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

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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