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Category:   Application (Security)  >   Clam AntiVirus Vendors:
Clam AntiVirus 'clamav-milter' Format String Flaw Lets Remote Users Execute Arbitrary Code
SecurityTracker Alert ID:  1008157
SecurityTracker URL:
CVE Reference:   CVE-2003-0946   (Links to External Site)
Updated:  Nov 19 2003
Original Entry Date:  Nov 12 2003
Impact:   Denial of service via network, Execution of arbitrary code via network, Root access via network, User access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): confirmed on 0.60 - 0.60p
Description:   A format string vulnerability was reported in Clam AntiVirus. A remote user can execute arbitrary code on the target system.

Secure Network Operations Strategic Reconnaissance Team reported that clamav-milter contains a format string flaw that can be exploited by a remote user if syslog support is configured.

A remote user can send an e-mail with a specially crafted "From:" address containing "%" characters and with e-mail content that will trigger a virus rule to the target system. In this case, the remote user's e-mail address will be passed to syslog() without appropriate validation. The syslog call is reportedly made without a format specifier. A remote user can cause the target Clam AntiVirus software to crash or to execute arbitrary code.

A demonstration exploit string is provided:

"mail from: %n%n%n%n%n%n%n"

Impact:   A remote user can cause the 'clamav-milter' process to crash or execute arbitrary code. The arbitrary code will run with the privileges of the Clam AntiVirus user or with root privileges, depending on how the system is configured.
Solution:   The vendor has released a fix in clamav-devel-20031111 and clamav-0.65, available at:

The author of the report indicates that you can, as a workaround, disable syslog support.

Vendor URL: (Links to External Site)
Cause:   Input validation error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   None.

 Source Message Contents

Subject:  SRT2003-11-11-1151 - clamav-milter remote exploit / DoS

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Secure Network Operations, Inc.   
Strategic Reconnaissance Team     
Team Lead Contact                 

Our Mission:
Secure Network Operations offers expertise in Networking, Intrusion 
Detection Systems (IDS), Software Security Validation, and 
Corporate/Private Network Security. Our mission is to facilitate a 
secure and reliable Internet and inter-enterprise communications 
infrastructure through the products and services we offer. 

To learn more about our company, products and services or to request a 
demo of ANVIL FCS please visit our site at, or 
call us at: 978-263-3829

Quick Summary:
Advisory Number         : SRT2003-11-11-1151
Product                 : Clam AntiVirus
Version                 : clamav-0.60 through clamav-0.60p
Vendor                  :
Class                   : Remote
Criticality             : High (to clamav-milter users)
Operating System(s)     : *nix, cygwin

The full technical details of this vulnerability can be found at: under the research section. 

Basic Explanation
High Level Description  : clamav-milter contains format strings issues.
What to do              : disable syslog support, upgrade to clamav-0.65

Basic Technical Details
Proof Of Concept Status : SNO has proof of concept. 

Low Level Description   : Clam AntiVirus is an anti-virus toolkit for 
UNIX. The main purpose of the software is to integrate with mail servers 
for attachment scanning. Clam AntiVirus works with Linux, Solaris, 
FreeBSD, OpenBSD, NetBSD, AIX, Mac OS X, and Cygwin B20.

Snapshot clamav-devel-20031111 and clamav-0.65 fix a potentially 
exploitable format string issue that can be triggered by a remote attacker. 
Only versions above clamav-0.54 that include syslog() functionality are 
vulnerable to this attack. CVS snapshots up to but not including version 
clamav-devel-20031111 may be vulnerable to attack. Versions clamav-0.60 
through clamav-0.60p are confirmed to be at least exploitable for a DoS 
condition. This issue only poses a problem for clamav-milter users.

*    0.60q   11/11/03 Fixed handling of % characters in e-mail addresses
*    pointed out by

This issue may potentially be used to run code as either the clamav user or
root depending on how clamav is configured. At the very least a DoS attack
on clamav-milter can be caused using "mail from: %n%n%n%n%n%n%n" along with 
a test antivirus string which is used to trigger an AV alert.

full details at

Vendor Status           : Promptly attended to the issue. Patched
clamav-milter is available in clamav-devel-20031111 and clamav-0.65

Bugtraq URL             : To be assigned. 
This advisory was released by Secure Network Operations,Inc. as a matter
of notification to help administrators protect their networks against
the described vulnerability. Exploit source code is no longer released
in our advisories but can be obtained under contract.. Contact our sales 
department at for further information on how to 
obtain proof of concept code.

Secure Network Operations, Inc. ||
"Embracing the future of technology, protecting you."




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