(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
(Links to External Site)
Date: Mar 29 2004
Host/resource access via network|
Fix Available: Yes Vendor Confirmed: Yes |
Version(s): Squid-2.x up to and including 2.5.STABLE4|
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://email@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.
A remote user may be able to submit a specially crafted URL to bypass url_regex access controls.|
Red Hat has issued a fix.|
Red Hat Linux 9:
The verification checksums are:
MD5 sum Package Name
Vendor URL: www.squid-cache.org/Advisories/SQUID-2004_1.txt (Links to External Site)
Access control error|
|Underlying OS: Linux (Red Hat Linux)|
|Underlying OS Comments: 9|
This archive entry is a follow-up to the message listed below.|
Source Message Contents
Subject: [Full-Disclosure] [RHSA-2004:134-01] Updated squid package fixes security vulnerability|
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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
CVE Names: CAN-2004-0189
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.
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
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:
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:
5. RPMs required:
Red Hat Linux 9:
MD5 sum Package Name
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:
The Red Hat security contact is <firstname.lastname@example.org>. More contact
details at https://www.redhat.com/solutions/security/news/contact.html
Copyright 2003 Red Hat, Inc.
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Full-Disclosure - We believe in it.