ESB-2018.3313 - [UNIX/Linux][BSD] Squid: Denial of service - Remote/unauthenticated 2018-10-29

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             AUSCERT External Security Bulletin Redistribution

                Squid Proxy Cache Security Update Advisory
                              29 October 2018


        AusCERT Security Bulletin Summary

Product:           Squid
Publisher:         Squid
Operating System:  UNIX variants (UNIX, Linux, OSX)
                   BSD variants
Impact/Access:     Denial of Service -- Remote/Unauthenticated
Resolution:        Patch/Upgrade

Original Bulletin:

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    Squid Proxy Cache Security Update Advisory SQUID-2018:5

Advisory ID:        SQUID-2018:5
Date:               October 28, 2018
Summary:            Denial of Service issue
                    in SNMP processing.
Affected versions:  Squid -> 3.5.28
                    Squid 4.x -> 4.3
Fixed in version:   Squid 4.4

Problem Description:

 Due to a memory leak in SNMP query rejection code, Squid is
 vulnerable to a denial of service attack.



 This problem allows a remote attacker to consume all memory
 available to the Squid process, causing it to crash.

 In environments where per-process memory restrictions are not
 enforced strictly, or configured to large values this may also
 affect other processes operating on the same machine. Leading to
 a much worse denial of service situation.

 This problem is limited to Squid built with SNMP support and
 receiving SNMP traffic.


Updated Packages:

 This bug is fixed by Squid version 4.4.

 In addition, patches addressing this problem for the stable
 releases can be found in our patch archives:

Squid 3.5:

Squid 4:

 If you are using a prepackaged version of Squid then please refer
 to the package vendor for availability information on updated


Determining if your version is vulnerable:

 All Squid built with --disable-snmp are not vulnerable.

 All Squid-2.x and older versions are not vulnerable.

 All Squid-3.x up to and including are not vulnerable.

 All Squid-3.x up to and including 3.5.28 configured with
 "snmp_port 0" are not vulnerable.

 All Squid-3.x up to and including 3.5.28 without snmp_port
 configured are not vulnerable.

 All Squid- and later 3.2.x versions with snmp_port
 configured to a non-0 value are vulnerable.

 All Squid-3.3 versions up to and including 3.3.14 with snmp_port
 configured to a non-0 value are vulnerable.

 All Squid-3.4 versions up to and including 3.4.14 with snmp_port
 configured to a non-0 value are vulnerable.

 All Squid-3.5 versions up to and including 3.5.28 with snmp_port
 configured to a non-0 value are vulnerable.

 All Squid-4.x versions up to and including 4.3 with snmp_port
 configured to a non-0 value are vulnerable.

To determine the version of your Squid and its build options use
the command:

 squid -v

To determine whether snmp_port is configured use the command:

 squid -k parse | grep snmp_port




 Enable firewall inspection of SNMP packets to enforce blocking
 of any non-permitted packets prior to their arriving at Squid.

 This restriction of packet sources reduces the risk, but does not
 completely remove the vulnerability.


 Remove snmp_port and related configuration settings until Squid
 can be upgraded to a fixed build.

 This completely removes the vulnerability at cost of reduced
 management and monitoring capabilities.


Contact details for the Squid project:

 For installation / upgrade support on binary packaged versions
 of Squid: Your first point of contact should be your binary
 package vendor.

 If your install and build Squid from the original Squid sources
 then the mailing list is your
 primary support point. For subscription details see

 For reporting of non-security bugs in the latest STABLE release
 the squid bugzilla database should be used

 For reporting of security sensitive bugs send an email to the mailing list. It's a closed
 list (though anyone can post) and security related bug reports
 are treated in confidence until the impact has been established.



 This vulnerability was discovered and fixed by Florian Kohnhäuser


Revision history:

 2018-10-23 06:15:46 UTC Initial Report
 2018-10-23 21:42:58 UTC Patch Released
 2018-10-27 21:19:00 UTC Packages Released

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