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From: advisories at corsaire.com (advisories) Subject: Corsaire Security Advisory: Multiple vendor HTTP user agent cookie path traversal issue -- Corsaire Security Advisory -- Title: Multiple vendor HTTP user agent cookie path traversal issue Date: 12.07.03 Application: Various Environment: Various Author: Martin O'Neal [martin.oneal@...saire.com] Audience: Vendor notification Reference: c030712-001 -- Scope -- The aim of this document is to clearly define a vulnerability in the cookie handling functionality of multiple vendors HTTP user agents that would allow an attacker to avoid the path restrictions specified by a cookie's originator. -- History -- Discovered: 08.07.03 Vendors notified: 12.07.03 - 18.07.03 RFC2965 authors notified: 29.07.03 CERT/CC notified: 20.08.03 Uncoordinated Opera release: 05.09.03 NISCC notified: 24.10.03 Document released: 10.03.04 -- Overview -- The cookie specifications detail a path argument that can be used to restrict the areas of a host that will be exposed to a cookie. By using standard traversal techniques this functionality can be subverted, potentially exposing the cookie to scrutiny and use in further attacks. -- Analysis -- The cookie standard is formally defined in RFC2965 [1]. This makes reference to the optional path argument that allows a cookie originator to specify "the subset of URLs on the origin server to which this cookie applies". Many of the user agents appear to function by simply string matching the initial part of the requested URL, so by using a combination of traversal and standard encoding techniques the path restriction functionality can be subverted. Where this oversight becomes useful is in conducting attacks against the session cookies of an application that does not suffer from any exploitable validation flaws, but that shares the same server environment with one that does. It is worth acknowledging that whilst many client applications still suffer from "same origin" issues then this is something of a moot point anyway. -- Proof of concept -- This proof of concept is known to work with the current releases of the major browsers. For this example we shall imagine that our secure application shares a host with some sample files that were installed at the same time as the web server. Obviously, this would never happen in a live production environment (pauses to insert tongue firmly in cheek). The secure application is located within the "/secure" folder and sets the cookie path argument to "/secure" which is intended to restrict the cookie information from being exposed elsewhere on the same host. The attacker knows that the secure application has no useable vulnerabilities in itself and can also see that the cookie that it sets has the path restricted. They also know that the sample files have an exploitable XSS flaw that would give them access to the all-important session cookies (if they can get a valid user to access it; a completely different problem to solve). A lot of browsers will make a URI canonical before passing it to the target server, resolving any redundant directory traversal prior to dispatch. By using an encoded URL the attacker can defeat this functionality, bypass the path restriction intended by the originator and get the valid users browser to expose the session cookie to the sample application: http://host/secure/%2e%2e/sample/insecure.cgi?xss=<golarge> -- Recommendations -- The cookie path functionality of the affected user agents should be revised to ensure that they work as intended and cannot be bypassed by traversal and encoding techniques. Many of the vendors involved have silently patched this issue in product releases made after July 2003. Check with the individual vendor for additional information. -- CVE -- The Common Vulnerabilities and Exposures (CVE) project has assigned multiple names to this issue: CAN-2003-0513 Microsoft Internet Explorer cookie path traversal issue CAN-2003-0514 Apple Safari cookie path traversal issue CAN-2003-0592 KDE Konqueror cookie path traversal issue CAN-2003-0593 Opera cookie path traversal issue CAN-2003-0594 Mozilla cookie path traversal issue These are candidates for inclusion in the CVE list, which standardises names for security problems (http://cve.mitre.org), -- References -- [1] http://www.faqs.org/rfcs/rfc2965.html -- Revision -- a. Initial release. b. Minor revision. c. Amended history section. d. Amended history section. e. Amended recommendations section. f. Released. -- Distribution -- This security advisory may be freely distributed, provided that it remains unaltered and in its original form. -- Disclaimer -- The information contained within this advisory is supplied "as-is" with no warranties or guarantees of fitness of use or otherwise. Corsaire accepts no responsibility for any damage caused by the use or misuse of this information. Copyright 2003 Corsaire Limited. All rights reserved. -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.grok.org.uk/pipermail/full-disclosure/attachments/20040310/ecbc2d5c/attachment.html
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