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Category:   Application (Generic)  >   Squid Vendors:   Squid-cache.org
Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
SecurityTracker Alert ID:  1011614
SecurityTracker URL:  http://securitytracker.com/id/1011614
CVE Reference:   CVE-2004-0918   (Links to External Site)
Date:  Oct 11 2004
Impact:   Denial of service via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): 2.5-STABLE6, 3.0-PRE3-20040702; when compiled with SNMP support
Description:   iDEFENSE reported a vulnerability in Squid in the SNMP service. A remote user can cause denial of service conditions.

It is reported that a remote user can supply a specially crafted SNMP packet to trigger an ASN1 parsing error and cause Squid to restart, dropping all current connections.

The flaw resides in the asn_parse_header() function in 'snmplib/asn1.c'.

The system is affected if compiled with SNMP support.

The vendor was notified on September 15, 2004.

The original advisory is available at:

http://www.idefense.com/application/poi/display?id=152&type=vulnerabilities

Impact:   A remote user can cause the proxy services to restart.
Solution:   The vendor has issued a fixed version (Squid-2.5.STABLE7), available at:

ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.gz
ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.bz2
http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.gz
http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.bz2

A patch for Squid-2.5.STABLE6 is also available:

http://www.squid-cache.org/Versions/v2/2.5/bugs/squid-2.5.STABLE6-SNMP_core_dump.patch

Vendor URL:  www.squid-cache.org/ (Links to External Site)
Cause:   Exception handling error, Input validation error
Underlying OS:  Linux (Any), UNIX (Any)

Message History:   This archive entry has one or more follow-up message(s) listed below.
Oct 14 2004 (Fedora Issues Fix for FC2) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Fedora has released a fix for Fedora Core 2.
Oct 19 2004 (Gentoo Issues Fix) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Gentoo has released a fix.
Oct 20 2004 (Red Hat Issues Fix) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Red Hat has released a fix for Red Hat Enterprise Linxu 2.1 and 3.
Oct 21 2004 (Mandrake Issues Fix) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Mandrake has released a fix.
Oct 25 2004 (Vendor Issues Advisory) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
The vendor has issued their advisory.
Oct 29 2004 (Debian Issues Fix) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Debian has released a fix.
Nov 3 2004 (Conectiva Issues Fix) Squid SNMP Parsing Error Lets Remote Users Restart the Proxy Server
Conectiva has released a fix.



 Source Message Contents

Subject:  iDEFENSE Security Advisory 10.11.04: Squid Web Proxy Cache Remote


Squid Web Proxy Cache Remote Denial of Service Vulnerability

iDEFENSE Security Advisory 10.11.04:
www.idefense.com/application/poi/display?id=152&type=vulnerabilities
October 11, 2004

I. BACKGROUND

Squid Web Proxy Cache is a full-featured web proxy cache designed to run
on Unix systems. It supports proxying HTTP, FTP, SSL, DNS, and has
support for SNMP.

II. DESCRIPTION

Remote exploitation of a design error in the SNMP module of Squid Web
Proxy Cache may lead to a denial of service.

The problem specifically exists due to an ASN1 parsing error where
certain header length combinations can slip through the validations
performed by the ASN1 parser, eventually causing the server to restart
and close all current connections. The server takes several seconds to
restart.

The offending code is in the asn_parse_header() routine of
snmplib/asn1.c, which under some cases will allow negative length fields
to pass validation. This leads to a failed xmalloc(), and the server
then assumes there is heap corruption or some other exceptional
condition, and restarts.

III. ANALYSIS

An attacker can exploit the above-described vulnerability to crash a
Squid server. If the attack is repeated, it can render the server
useless. Only a single UDP packet is required to trigger this
vulnerability, so the source address can be spoofed.

IV. DETECTION

iDEFENSE has confirmed the existence of this vulnerability in Squid Web
Proxy Cache version 2.5-STABLE5 compiled with SNMP support as well as
Squid Web Proxy Cache version 3.0-PRE3-20040702 compiled with SNMP
support. It is suspected that earlier versions are vulnerable as well.

To find if a Squid binary is compiled with SNMP support one can run:

    grep snmp_port /usr/local/squid/sbin/squid

If this command returns silently, that binary was not built with SNMP
support and it is not vulnerable to this issue.

V. WORKAROUND

Disable SNMP support or filter the port that has SNMP processing
activated (3401 by default) to allow only SNMP data from trusted hosts.

To disable SNMP support on a squid binary that has SNMP support compiled
in, use the entry snmp_port 0 in the squid.conf configuration file.

To allow only the local interface to process SNMP, use the entry
"snmp_incoming_address 127.0.0.1" in the squid.conf configuration file.

Squid must be restarted to activate changes in the configuration file.

VI. VENDOR RESPONSE

Patch relative to Squid-2.5.STABLE6:

=20
http://www.squid-cache.org/Versions/v2/2.5/bugs/squid-2.5.STABLE6-SNMP_c
ore_dump.patch

Squid-2.5.STABLE7 release:

   ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.gz
=20
ftp://ftp.squid-cache.org/pub/squid-2/STABLE/squid-2.5.STABLE7.tar.bz2
   http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.gz
   http://www.squid-cache.org/Versions/v2/2.5/squid-2.5.STABLE7.tar.bz2

or any of the mirrors

   http://www.squid-cache.org/Mirrors/ftp-mirrors.html
   http://www.squid-cache.org/Mirrors/http-mirrors.html

VII. CVE INFORMATION

The Common Vulnerabilities and Exposures (CVE) project has assigned the
names CAN-2004-0918 to these issues. This is a candidate for inclusion
in the CVE list (http://cve.mitre.org), which standardizes names for
security problems.

VIII. DISCLOSURE TIMELINE

09/15/2004  Initial vendor notification
09/15/2004  iDEFENSE clients notified
09/15/2004  Initial vendor response
10/05/2004  Coordinated public disclosure

IX. CREDIT

The discoverer of this vulnerability wishes to remain anonymous.

Get paid for vulnerability research
http://www.idefense.com/poi/teams/vcp.jsp

X. LEGAL NOTICES

Copyright (c) 2004 iDEFENSE, Inc.

Permission is granted for the redistribution of this alert
electronically. It may not be edited in any way without the express
written consent of iDEFENSE. If you wish to reprint the whole or any
part of this alert in any other medium other than electronically, please
email customerservice@idefense.com for permission.

Disclaimer: The information in the advisory is believed to be accurate
at the time of publishing based on currently available information. Use
of the information constitutes acceptance for use in an AS IS condition.
There are no warranties with regard to this information. Neither the
author nor the publisher accepts any liability for any direct, indirect,
or consequential loss or damage arising from use of, or reliance on,
this information.
 
 


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