Squid Proxy Cache Security Update Advisory SQUID-2023:1

Advisory ID:       | SQUID-2023:1
Date:              | October 22, 2023
Summary:           | Request/Response smuggling in HTTP(S) and ICAP
Affected versions: | Squid 2.6.STABLE10  -> 2.7.STABLE9
                   | Squid 3.x -> 3.5.28
                   | Squid 4.x -> 4.16
                   | Squid 5.x -> 5.9
                   | Squid 6.x -> 6.3
Fixed in version:  | Squid 6.4

Problem Description:

 Due to chunked decoder lenience Squid is vulnerable to
 Request/Response smuggling attacks when parsing HTTP/1.1
 and ICAP messages.



 This problem allows a remote attacker to perform
 Request/Response smuggling past firewall and frontend security
 systems when the upstream server interprets the chunked encoding
 syntax differently from Squid.

 This attack is limited to the HTTP/1.1 and ICAP protocols which
 support receiving Transfer-Encoding:chunked.

CVSS Score of 9.3


Updated Packages:

#This bug is fixed by Squid version 6.4.

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

Squid 5:

Squid 6:

 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:

 Squid older than 5.1 have not been tested and should be
 assumed to be vulnerable.

 All Squid-5.x up to and including 5.9 are vulnerable.

 All Squid-6.x up to and including 6.3 are vulnerable.



 * ICAP issues can be reduced by ensuring only trusted ICAP
   services are used, with TLS encrypted connections
   (ICAPS extension).

 *  There is no workaround for the HTTP Request Smuggling issue.


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 you install and build Squid from the original Squid sources
 then the <squid-us...@lists.squid-cache.org> 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
 <squid-b...@lists.squid-cache.org> 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 by Keran Mu and Jianjun Chen,
 from Tsinghua University and Zhongguancun Laboratory.

 Fixed by Amos Jeffries of Treehouse Networks Ltd.


Revision history:

 2023-09-01 04:34:00 UTC Initial Report
 2023-10-01 08:43:00 UTC Patch Available
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