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AUSCERT External Security Bulletin Redistribution
Squid Proxy Cache Security Update Advisory SQUID-2016:2
29 February 2016
AusCERT Security Bulletin Summary
Operating System: Windows
UNIX variants (UNIX, Linux, OSX)
Impact/Access: Denial of Service -- Remote/Unauthenticated
CVE Names: CVE-2016-2572 CVE-2016-2571 CVE-2016-2570
Comment: This advisory references vulnerabilities in products which run on
platforms other than Squid. It is recommended that administrators
running Squid check for an updated version of the software for their
Revision History: February 29 2016: CVEs assigned to vulnerabilities
February 25 2016: Initial Release
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Squid Proxy Cache Security Update Advisory SQUID-2016:2
Advisory ID: SQUID-2016:1
Date: February 23, 2016
Summary: Multiple Denial of Service issues
in HTTP Response processing.
Affected versions: Squid 3.x -> 3.5.16
Squid 4.x -> 4.0.7
Fixed in version: Squid 4.0.7, 3.5.15
Due to incorrect bounds checking Squid is vulnerable to a denial
of service attack when processing HTTP responses.
Due to incorrect error handling Squid-4 is vulnerable to a denial
of service attack when processing malformed HTTP responses.
These problems allow remote servers delivering certain unusual
HTTP response syntax to trigger a denial of service for all
clients accessing the Squid service.
HTTP responses containing malformed headers that trigger this
issue are becoming common. We are not certain at this time if
that is a sign of malware or just broken server scripting.
Details of a trivial attack are already circulating publicly.
These bugs are fixed by Squid version 3.5.15 and 4.0.7.
In addition, patches addressing these problems for the stable
release can be found in our patch archives:
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-3.2 and older have not been tested but are expected to
All unpatched Squid-3.3 versions are vulnerable.
All unpatched Squid-3.4 versions are vulnerable.
All unpatched Squid-3.5.14 and older are vulnerable.
All unpatched Squid-4.0.6 and older are vulnerable.
There are no good workarounds known for these vulnerabilities.
The following squid.conf settings can protect Squid-3.5 (only)
against the publicly published attack. But unpatched Squid
remain vulnerable to other known attacks:
acl Vary rep_header Vary .
store_miss deny Vary
The following squid.conf settings can protect against the
publicly published attack. But unpatched Squid remain vulnerable
to other known attacks:
cache deny all
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
If your install and build Squid from the original Squid sources
then the email@example.com 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
firstname.lastname@example.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.
CVE-2016-2569 bounds checking vulnerability was identified and
reported by Mathias Fischer from Open Systems AG.
Fixed by Alex Rousskov from The Measurement Factory.
CVE-2016-2571, CVE-2016-2572 error handling vulnerability was
found and fixed by Alex Rousskov from The Measurement Factory.
CVE-2016-2570 bounds checking vulnerability was found and fixed
by William Lima.
2016-02-17 06:51:25 UTC Initial Report
2016-02-18 04:15:33 UTC Patches Released
2016-02-19 23:15:41 UTC Additional Patches Released
2016-02-23 16:37:27 UTC Attack PoC becomes public knowledge
2016-02-23 18:23:00 UTC Packages Released
2016-02-26 06:45:42 UTC CVE Assignment and additional patch referenced
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