July 9, 2002

Squid security advisory

Squid-Cache.org: "squid-2.4.STABLE7 has been released to address a number of
security issues in Squid and related software. All users of the
Squid HTTP Proxy are strongly encouraged to upgrade."

      Squid Proxy Cache Security Update Advisory SQUID-2002:3

Advisory ID:            SQUID-2002:3
Date:                   July 3, 2002
Summary:                Squid-2.4.STABLE7 released to address a
                        number of security related issues.
Affected versions:      Squid-2.x up to and including 2.4.STABLE6


Problem Description:

 squid-2.4.STABLE7 has been released to address a number of
 security issues in Squid and related software. All users of the
 Squid HTTP Proxy are strongly encouraged to upgrade.

 Security related changes in the 2.4.STABLE7 release:

 - Several bugfixes and cleanup of the Gopher client, both
   to correct some security issues and to make Squid properly
   render certain Gopher menus.
 - Security fixes in how Squid parses FTP directory listings into
 - FTP data channels are now sanity checked to match the address
   of the requested FTP server. This to prevent theft or injection
   of data. See the new ftp_sanitycheck directive if this sanity
   check is not desired.
 - The MSNT auth helper has been updated to v2.0.3+fixes for
   buffer overflow security issues found in this helper.
 - A security issue in how Squid forwards proxy authentication
   credentials has been fixed

 Other changes in the 2.4.STABLE7 release:

 - Squid now correctly rejects any requests using transfer-
   encoding. Squid is a HTTP/1.0 proxy and as such does not
   implement or support transfer-encoding.
 - Minor changes to support Apple MAC OS X and some other
   platforms more easily.
 - The client -T option has been implemented
 - HTCP related bugfixes in "squid -k reconfigure"

 For more details on the changes see the descriptions in our
 patch archive for version Squid-2.4.STABLE6:




 It is believed that several of the Gopher bug and the FTP
 directory parsing related bugs can be exploited to allow remote
 execution of code.

 The user executing the attack must be allowed to use the proxy
 for any potential attack to be successful, but it is believed
 that a remote attacker can use a small amount of social
 engineering to make an attack without direct access to the proxy.

 The third issue relating to FTP data channels is minor in nature
 in most installations, but there may be unfortunate interactions
 with firewalling policies etc making it a more severe issue than

 The MSNT auth helper issue is believed to possibly allow remote
 execution of code in certain configurations.

 The issue in forwarding of proxy authentication credentials may
 expose your users private proxy login+password to selected
 external web sites depending on your configuration.


Updated Packages:

 The Squid-2.4.STABLE7 release contains fixes for all these
 problems. You can download the Squid-2.4.STABLE7 release from


 or the mirrors (may take a while before all mirrors are updated).
 For a list of mirror sites see


 Individual patches to the mentioned issues can be found from our
 patch archive for version Squid-2.4.STABLE6


 The patches should also apply with only a minimal effort to
 earlier Squid 2.4 versions if required.

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


Determining if your version is vulnerable:

 To determine which version of Squid you are using, run the command

    squid -v

 You are likely to be vulnerable to these issues if you are
 running version 2.4.STABLE6 or earlier.

 If you are using a binary or otherwise pre-packaged version
 please verify with your vendor on which versions are affected as
 some vendors ship earlier versions with the needed patches
 applied.  Note that unless you have upgraded to a version
 released after 2002-07-01 you are  most likely vulnerable to
 these issues.

 There is no easy means to determine if your version is affected
 other than by the Squid version number.

 You may be vulnerable to the MSNT auth issue if your squid.conf
 file contains the directive

   authenticate_program /usr/local/squid/libexec/squid/msnt_auth

 and you have not upgraded your copy of msnt_auth to a corrected

 Note: msnt_auth is sometimes installed as msntauth, and the path
 may differ depending on the installation method.


Other versions of Squid:

 Versions prior to the 2.4 series are deprecated, please update
 to Squid-2.4.STABLE7 if you are using a version older than 2.4.

 Users of unreleased versions of squid (2.6.DEVEL or 2.5.PRE
 versions) should run the most recent version available to ensure
 that security issues arising during the development are addressed
 as quickly as possible. Furthermore, unreleased versions should
 not be used in a production environment.



 We recommend that you upgrade rather than try to workaround the
 issues by configuration. To most of the issues there is no easy
 workarounds that does not severely impact the functionality.

 The Gopher and FTP issues can be worked around by denying proxying
 of ftp:// or gopher:// URLs, for example by inserting the following
 lines at the top of your squid.conf

   # Workaround for bugs in Squid-2.4.STABLE6 and earlier
   acl workaround proto FTP Gopher
   http_access deny workaround

 The authentication credentials issue only applies if you are using
 proxy authentication, allow users access to some sites without
 the need to authenticate and you do not fully trust these sites or
 the network between these sites and the proxy. To work around the
 problem make sure your users needs to authenticate on all sites or

 If you are using the msnt_auth authentication helper then you are
 only vulnerable if you are using the allowusers or denyusers
 extension of msnt_auth. To work around this defiance of msnt_auth
 you can use the proxy_auth acl type to specify the valid users
 and delete the allowusers and denyusers files.


Contact details for the squid project:

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

 If your install is built from the original squid sources, then
 the squid-users@squid-cache.org mailing list is your primary
 support point. (see 
 for subscription details).

 For bug reporting, particularly security related bugs the
 squid-bugs@squid-cache.org mailing list is the appropriate forum.
 It's a closed list (though anyone can post) and security related
 bug reports are treated in confidence until the impact has been
 established. For non security related bugs, the squid bugzilla
 database should be used .



 Olaf Kirch (formerly @ Caldera), for reporting the FTP and Gopher
 related issues

 MARA Systems AB, for sponsoring the development of patches to the
 FTP, Gopher, authentication and transfer encoding issues.

 Duane Wessels, for fixes to the MSNT auth helper


Revision history:

 2002-07-03 21:10 GMT Initial release


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