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AUSCERT External Security Bulletin Redistribution
ESB-2002.332 -- Squid Proxy Cache Security Update Advisory SQUID-2002:3
Squid-2.4.STABLE7 released to address a number of security related issues
5 July 2002
AusCERT Security Bulletin Summary
Product: Squid-2.x up to and including 2.4.STABLE6
Impact: Execute Arbitrary Code/Commands
Access Confidential Data
Access Required: Remote
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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
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.
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
Determining if your version is vulnerable:
To determine which version of Squid you are using, run the command
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
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
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 firstname.lastname@example.org mailing list is your primary
support point. (see <http://www.squid-cache.org/mailing-lists.html>
for subscription details).
For bug reporting, particularly security related bugs the
email@example.com 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 <http://www.squid-cache.org/bugs/>.
Olaf Kirch (formerly @ Caldera), for reporting the FTP and Gopher
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
2002-07-03 21:10 GMT Initial release
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