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Category:   Application (Generic)  >   Squid Vendors:   Squid-cache.org
(Red Hat Issues Fix for RH Linux) Squid Proxy Cache '%00' URL Character Access Control Bug May Let Remote Users Bypass Certain Access Controls
SecurityTracker Alert ID:  1009580
SecurityTracker URL:  http://securitytracker.com/id/1009580
CVE Reference:   CVE-2004-0189   (Links to External Site)
Date:  Mar 29 2004
Impact:   Host/resource access via network
Fix Available:  Yes  Vendor Confirmed:  Yes  
Version(s): Squid-2.x up to and including 2.5.STABLE4
Description:   A vulnerability was reported in the Squid Proxy Cache server in the processing of URLs containing '%00'. A remote user may be able to bypass certain access controls.

It is reported that a flaw in the '%xx' URL decoding function may allow a remote user to bypass access controls that use 'url_regex' access control list (ACL) types. The report indicates that Squid will insert a NUL character in place of '%00' in a URL before analyzing the URL for access control purposes. As a result, the 'http://foo%00@www.example.com/' URL will not be properly detected as a URL to be denied in accordance with the following type of access control configuration:

acl BadSite url_regex www\.example\.com
http_access deny BadSite

In this example, Squid will attempt to compare 'http://foo' with 'www\.example\.com' and will not find a match, so the URL will not be denied.

Mitch Adair is credited with reporting this flaw.

Impact:   A remote user may be able to submit a specially crafted URL to bypass url_regex access controls.
Solution:   Red Hat has issued a fix.

Red Hat Linux 9:

SRPMS:
ftp://updates.redhat.com/9/en/os/SRPMS/squid-2.5.STABLE1-3.9.src.rpm

i386:
ftp://updates.redhat.com/9/en/os/i386/squid-2.5.STABLE1-3.9.i386.rpm

The verification checksums are:

MD5 sum Package Name

3a78ab4b0423bdbfc5b6bb36897b78ce 9/en/os/SRPMS/squid-2.5.STABLE1-3.9.src.rpm
348ca4845204fadad07116be64d9767e 9/en/os/i386/squid-2.5.STABLE1-3.9.i386.rpm

Vendor URL:  www.squid-cache.org/Advisories/SQUID-2004_1.txt (Links to External Site)
Cause:   Access control error
Underlying OS:  Linux (Red Hat Linux)
Underlying OS Comments:  9

Message History:   This archive entry is a follow-up to the message listed below.
Mar 1 2004 Squid Proxy Cache '%00' URL Character Access Control Bug May Let Remote Users Bypass Certain Access Controls



 Source Message Contents

Subject:  [Full-Disclosure] [RHSA-2004:134-01] Updated squid package fixes security vulnerability


-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

- ---------------------------------------------------------------------
                   Red Hat Security Advisory

Synopsis:          Updated squid package fixes security vulnerability
Advisory ID:       RHSA-2004:134-01
Issue date:        2004-03-29
Updated on:        2004-03-29
Product:           Red Hat Linux
Keywords:          phishing spoofing
Cross references:  
Obsoletes:         
CVE Names:         CAN-2004-0189
- ---------------------------------------------------------------------

1. Topic:

An updated squid package is avaliable that fixes a security vulnerability in
URL decoding and provides a new ACL type for protecting vulnerable clients.

2. Relevant releases/architectures:

Red Hat Linux 9 - i386

3. Problem description:

Squid is a full-featured Web proxy cache.

A bug was found in the processing of %-encoded characters in a URL in
versions of Squid 2.5.STABLE4 and earlier.  If a Squid configuration uses
Access Control Lists (ACLs), a remote attacker could create URLs that would
not be correctly tested against Squid's ACLs, potentially allowing clients
to access prohibited URLs.

Users of Squid should update to these erratum packages which are not
vulnerable to this issue.

In addition, these packages contain a new Access Control type, "urllogin",
which can be used to protect vulnerable Microsoft Internet Explorer clients
from accessing URLs that contain login information.  Such URLs are often
used by fraudsters to trick web users into revealing valuable personal data.

Note that the default Squid configuration does not make use of this new
access control type.  You must explicitly configure Squid with ACLs that
use this new type, in accordance with your own site policies.

4. Solution:

Before applying this update, make sure all previously released errata
relevant to your system have been applied.

To update all RPMs for your particular architecture, run:

rpm -Fvh [filenames]

where [filenames] is a list of the RPMs you wish to upgrade.  Only those
RPMs which are currently installed will be updated.  Those RPMs which are
not installed but included in the list will not be updated.  Note that you
can also use wildcards (*.rpm) if your current directory *only* contains the
desired RPMs.

Please note that this update is also available via Red Hat Network.  Many
people find this an easier way to apply updates.  To use Red Hat Network,
launch the Red Hat Update Agent with the following command:

up2date

This will start an interactive process that will result in the appropriate
RPMs being upgraded on your system.

If up2date fails to connect to Red Hat Network due to SSL
Certificate Errors, you need to install a version of the
up2date client with an updated certificate.  The latest version of
up2date is available from the Red Hat FTP site and may also be
downloaded directly from the RHN website:

https://rhn.redhat.com/help/latest-up2date.pxt

5. RPMs required:

Red Hat Linux 9:

SRPMS:
ftp://updates.redhat.com/9/en/os/SRPMS/squid-2.5.STABLE1-3.9.src.rpm

i386:
ftp://updates.redhat.com/9/en/os/i386/squid-2.5.STABLE1-3.9.i386.rpm



6. Verificationx:

MD5 sum                          Package Name
- --------------------------------------------------------------------------

3a78ab4b0423bdbfc5b6bb36897b78ce 9/en/os/SRPMS/squid-2.5.STABLE1-3.9.src.rpm
348ca4845204fadad07116be64d9767e 9/en/os/i386/squid-2.5.STABLE1-3.9.i386.rpm

These packages are GPG signed by Red Hat for security.  Our key is
available from https://www.redhat.com/security/keys.html

You can verify each package with the following command:
    
    rpm --checksig -v <filename>

If you only wish to verify that each package has not been corrupted or
tampered with, examine only the md5sum with the following command:
    
    md5sum <filename>


7. References:

http://www.squid-cache.org/Advisories/SQUID-2004_1.txt
http://www.microsoft.com/security/incident/spoof.asp
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CAN-2004-0189

8. Contact:

The Red Hat security contact is <secalert@redhat.com>.  More contact
details at https://www.redhat.com/solutions/security/news/contact.html

Copyright 2003 Red Hat, Inc.
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Version: GnuPG v1.0.7 (GNU/Linux)

iD8DBQFAZ8wiXlSAg2UNWIIRAvLtAJ9m80AQ+tBgHykXISFZ5ciVWsDTHwCgoMmE
Fus3c5uYE8a3WsKyXikuM9A=
=pl9C
-----END PGP SIGNATURE-----

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.netsys.com/full-disclosure-charter.html

 
 


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