Software Engineering Institute

Updated:  March 21, 2006

Status

Affected

Vendor Statement

Subject:       XSS Vulnerability in Pubcookie Login Server
Author:        Nathan Dors, Pubcookie Project
Status:        Confirmed, Patches Released
Threat Class:  Cross-Site Scripting
Issue date:    March 6, 2006
Severity:      Critical

Summary:
========

New releases of Pubcookie are available to address Cross-Site Scripting
(XSS) vulnerabilities found in the Pubcookie login server.

Sites running a Pubcookie login server are strongly advised to read this
security advisory and carry out the suggested actions below.

Note: The URL for this security advisory is:
http://pubcookie.org/news/20060306-login-secadv.html

Background:
===========

XSS vulnerabilities typically involve three principals: a vulnerable Web
site, an attacker, and an end-user.  The attacker exploits the
vulnerability in the Web site such that script written by the attacker
is run by the user within the security context of the Web site.

XSS vulnerabilities can be classified as persistent or non-persistent,
depending on whether or not the script or HTML injected by the attacker
persists on the vulnerable Web site.

A persistent XSS vulerability allows the attacker to leave script or
HTML on the vulnerable Web site where it has the potential of being run
by multiple users without further involvement by the attacker. Blogs and
message boards are example places where persistent XSS vulnerabilities
are often exploited.

A non-persistent XSS vulnerability, on the other hand, doesn't allow the
attacker to stage script or HTML on the vulnerable Web site. Instead, he
or she must stage it elsewhere and then orchestrate some other means of
initiating the attack, very often requiring the user's unintentional
cooperation. Email, chat messages, and web pages are example places
where script might be staged to help exploit a non-persistent XSS
vulnerability. The user might trigger the attack simply by opening a
tainted message or Web page, or by clicking inadvertently on a tainted
link.

Pubcookie Login Server Details:
===============================

Multiple non-persistent XSS vulnerabilities were found in the Pubcookie
login server's compiled binary "index.cgi" CGI program. The CGI program
mishandles untrusted data when printing responses to the browser. This
makes the program vulnerable to carefully crafted requests containing
script or HTML. If an attacker can lure an unsuspecting user to visit
carefully staged content, the attacker can use it to redirect the user
to his or her local Pubcookie login page and attempt to exploit the XSS
vulnerabilities.

Threat Classification:
======================

These vulnerabilities are classified as *critical* due to the nature and
purpose of the Pubcookie login server for user authentication and Web
Single Sign-on (SSO). Specific threats include:

*) An attacker who injects malicious script through the vulnerabilities
might steal senstive user data including a user's authentication
credentials (usernames and passwords);

*) An attacker who injects malicious script through the vulnerabilities
might steal private Pubcookie data including a user's authentication
assertion ("granting") cookies and SSO ("login") session cookies;

*) An attacker who injects HTML tags through the vulnerabilities might
deface a site's Pubcookie login page for a single visit by a single user
(i.e. a non-persistent defacement).

At the heart of these threats lies a violation of the user's trust in
the Pubcookie login server.

Affected Versions:
==================

This advisory applies to all versions of the Pubcookie login server's
"index.cgi" compiled binary CGI program.

The following releases (including beta and final releases) are known to
be affected: 3.0.0, 3.1.0, 3.1.1, 3.2.0, 3.2.1, 3.2.1a and 3.3.0.

Patch Releases:
===============

The following patch releases address all known XSS vulnerabilities:
* 3.3.0a (current production release)
* 3.2.1b

These releases are available now from the project's dowloads page:
* http://pubcookie.org/downloads.html

Patch files are also available for versions 3.3.0 and 3.2.1a from:
* http://pubcookie.org/downloads/

Patch file names are:
* pbc-login-server-security-fix-3_3_0-3_3_0a.patch
* pbc-login-server-security-fix-3_2_1a-3_2_1b.patch

Note: the login server security patch files include source code fixes
for the login server's "index.cgi" compiled binary CGI program and for
several accompanying HTML template files.

Suggested Action:
=================

All sites running a Pubcookie login server are strongly advised to
pursue the following course of action:

1) Sites using a 3.0 or 3.1 login server should upgrade to one of the
current patch releases. Version 3.3.0a (current production release) is
recommended.

2) Sites using a 3.2 login server should, at minimum, upgrade to the
patched 3.2.1b release. Sites should also consider upgrading to 3.3.0a.

3) Sites using a 3.3 login server should upgrade to the patched 3.3.0a
release.

4) Sites using locally modified versions of the login server should
apply and integrate the login server security patch that most closely
matches the local version.

Note: For detailed version compatibility notes and upgrade information,
consult the relevant Pubcookie login server administration guide online.

Project Response:
=================

* 18 Dec 2005: Vulnerabilities discovered.
* 18 Dec 2005: Initial contact with technical details of vulnerability.
* 18 Dec 2005: Initial response confirming exploit and severity.
* 05 Jan 2006: Initial patches available for hardness testing.
* 06 Feb 2006: Solutions available for all known vulnerabilities.
* xx Mar 2006: Coordinated public release of security advisory.

Acknowledgements:
=================

The Pubcookie project wishes to thank Ben Maurer of Carnegie Mellon
University for reporting the original XSS vulnerability and for advising
during the fixes.

The Pubcookie project also wishes to thank the following sites for their
participation in the security response: University of Wisconsin-Madison,
Carnegie Mellon University, Stockholm University, University of
Virigina, University of Washington.

References:
===========

Web Security Threat Classification
http://www.webappsec.org/projects/threat/

CERT Advisory CA-2000-02 Malicious HTML Tags Embedded in Client Web
Requests
http://www.cert.org/advisories/CA-2000-02.html

Phishing With Super Bait
http://www.whitehatsec.com/presentations/phishing_superbait.pdf

XSS (Cross Site Scripting) Cheat Sheet
http://ha.ckers.org/xss.html

Vendor Information

The vendor has not provided us with any further information regarding this vulnerability.