University of Washington

Updated:  March 21, 2006



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: 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: * Patch files are also available for versions 3.3.0 and 3.2.1a from: * 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 CERT Advisory CA-2000-02 Malicious HTML Tags Embedded in Client Web Requests Phishing With Super Bait XSS (Cross Site Scripting) Cheat Sheet

Vendor Information

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