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Date Published: November 28, 2000



Title: Remote File Attachment Theft via comm.lycos.com,angelfire.com,

eudoramail.com



Class: Access Validation Error



Remotely Exploitable: Yes



Vulnerability Description:



WebMail (possibly WhoWhere.com software) as installed on

comm.lycos.com, angelfire.com, eudoramail.com and others allows an

attacker to hijack other people's attachments by modifying the hidden

form fields on the compose message form. If a file is attached to a

message, the compose message form has a hidden form field that looks

something like this:



filename.txt = /tmp/cache/24377.550



By setting it to a similar value, one can send email containing

someone else's attachments. For example:



filename.txt = /tmp/cache/24377.549



It was also possible to do ../..-style directory transversal.



The nature of the problem lies in the following:



1. User is allowed to reference attachments belonging to other users,

that is, there were no file-ownership checks.

2. User input was not validated for ".." character sequences.

3. Naming of temporary files followed an easy-to-predict numbering

scheme.



Technical Description - Exploit/Concept Code:



This problem is trivial to exploit by hand by saving the compose

message HTML form locally and modifying it. However, it is imperative

to note that enforcing strict user-agent, cookie and referer check

does not prevent such vulnerabilities from being exploited. There are

publicly available tools (Such as The ELZA at www.stoev.org) that

allow for the exploitation of such vulnerabilities, while preserving

stealth behavior with respect to cookies, referers and user-agent

strings to the extent required to keep the web site software happy.



Solution/Vendor Information/Workaround:



The vendor has fixed this particular problem, however all web mail

vendors are hereby urged to evaluate their systems for similar

problems.



Vendor notified on: November 8, 2000



Credits: This vulnerability was discovered and reported by Philip

Stoev .



This advisory was drafted with the help of the SecurityFocus.com

Vulnerability Help Team. For more information or assistance drafting

advisories please mail vulnhelp@securityfocus.com.



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