Squid Proxy Cache Security Update Advisory SQUID-2019:12

Advisory ID:        SQUID-2019:12
Date:               April 23, 2020
Summary:            Multiple issues
                    in ESI Response processing.
Affected versions:  Squid 3.x -> 3.5.28
                    Squid 4.x -> 4.10
                    Squid 5.x -> 5.0.1
Fixed in version:   Squid 4.11 and 5.0.2


Problem Description:

 Due to incorrect buffer handling Squid is vulnerable to cache
 poisoning, remote execution, and denial of service attacks when
 processing ESI responses.



 These problems allow a remote server delivering certain ESI
 response syntax to trigger a buffer overflow.

 On systems with heap overflow protection overflow will shutdown
 the proxy causing a denial of service for all clients accessing
 the Squid service.

 On systems with ESI buffer pooling (the default) overflow will
 truncate portions of generated payloads. Poisoning the HTTP
 response cache with corrupted objects.

 The CVE-2019-12519 issue also overwrites arbitrary attacker
 controlled information onto the process stack. Allowing remote
 code execution with certain crafted ESI payloads.

 These problems are restricted to ESI responses received from an
 upstream server. Attackers have to compromise the server or
 transmission channel to utilize these vulnerabilities.


Updated Packages:

 This bug is fixed by Squid versions 4.11 and 5.0.2.

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

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-2.x are not vulnerable.

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

 All Squid-3.0 versions built without --enable-esi are not

 All Squid-3.x versions built with --enable-esi are vulnerable.

 All Squid-4.x up to and including Squid-4.10 are vulnerable.

 Squid-5.0.1 is not vulnerable to the CVE-2019-12519 remote code
 execution issue.

 Squid-5.0.1 is vulnerable to the CVE-2019-12521 issues.



 Build Squid with --disable-esi


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 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 Jeriko One

 Fixed by Amos Jeffries of Treehouse Networks Ltd.


Revision history:

 2019-05-14 14:56:49 UTC Initial Report
 2019-05-20 11:23:13 UTC Patches Released
 2019-06-05 15:52:17 UTC CVE Assignment
 2020-04-23 08:00:00 UTC Advisory Released
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