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Squid Proxy Cache Security Update Advisory SQUID-2016:1
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Advisory ID: SQUID-2016:1
Date: February 16, 2016
Summary: Remote Denial of Service issue
in SSL/TLS processing.
Affected versions: Squid 3.5.13
Squid 4.0.4 -> 4.0.5
Fixed in version: Squid 4.0.6, 3.5.14
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http://www.squid-cache.org/Advisories/SQUID-2016_1.txt
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Problem Description:
Due to incorrectly handling server errors Squid is vulnerable to
a denial of service attack when connecting to TLS or SSL servers.
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Severity:
This problem allows any trusted client to perform a denial of
service attack on the Squid service regardless of whether TLS or
SSL is configured for use in the proxy.
Misconfigured client or server software may trigger this issue
to perform a denial of service unintentionally.
However, the bug is exploitable only if Squid is built using the
--with-openssl option.
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Updated Packages:
These bugs are fixed by Squid version 3.5.14 and 4.0.6.
In addition, patches addressing this problem for stable releases
can be found in our patch archives:
Squid 3.5:
http://www.squid-cache.org/Versions/v3/3.5/changesets/squid-3.5-13981.patch
If you are using a prepackaged version of Squid then please refer
to the package vendor for availability information on updated
packages.
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Determining if your version is vulnerable:
All Squid-3.4 and older versions are not vulnerable.
All Squid-3.5.12 and older 3.5 versions are not vulnerable.
All Squid-3.5 built without OpenSSL support are not vulnerable.
All Squid-4.0.3 and older 4.0 versions are not vulnerable.
All Squid-4 built without OpenSSL support are not vulnerable.
All unpatched Squid-3.5.13, 4.0.4, and 4.0.5 built using
--with-openssl are vulnerable.
The following command can be used to easily determine if a
vulnerable build is being used:
squid -v
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Workaround:
Disabling service for https:// URLs entirely at the top of the
squid.conf http_access rules fully protects against this
vulnerability:
acl HTTPS proto HTTPS
http_access deny HTTPS
Or,
Relaying outbound HTTPS traffic through a non-vulnerable proxy
protects against the issue unless the SSL-bump splice feature is
being used.
Or,
Disabling service for irregular HTTPS ports protects against the
simplest forms of attack while retaining most HTTPS service:
acl HTTPS proto HTTPS
http_access deny HTTPS !SSL_Ports
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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-users@xxxxxxxxxxxxxxxxxxxxx mailing list is your
primary support point. For subscription details see
<http://www.squid-cache.org/Support/mailing-lists.html>.
For reporting of non-security bugs in the latest STABLE release
the squid bugzilla database should be used
<http://bugs.squid-cache.org/>.
For reporting of security sensitive bugs send an email to the
squid-bugs@xxxxxxxxxxxxxxxxxxxxx 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.
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Credits:
The vulnerability was reported and fixed by Christos Tsantilas of
The Measurement Factory.
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Revision history:
2016-02-12 17:50:38 GMT Initial Report
2016-02-12 18:05:44 GMT Patch Released
2016-02-15 17:15:00 GMT Packages Released
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END
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