Rapid7 Advisory R7-0033: Apache HTTP Server mod_proxy_ftp Wildcard Characters Cross-Site Scripting

August 5, 2008 - The mod_proxy_ftp module of the Apache HTTP Server is vulnerable to a cross-site scripting vulnerability when handling requests with wildcard characters (aka globbing characters).

Affected system(s):

KNOWN VULNERABLE:

• Apache HTTP Server 2.2.9 (and earlier 2.2.x versions)
• Apache HTTP Server 2.0.63 (and earlier 2.0.x versions)

NOT VULNERABLE:

• Apache HTTP Server 1.3.x (because mod_proxy_ftp doesn't support wildcard characters)

Apache HTTP Server Project
http://httpd.apache.org

The developers were notified of this vulnerability on July 28, 2008 via the private security mailing list security@apache.org. They acknowledged it within 12 hours. On July 29, they assigned it a CVE ID. On August 5, the vulnerability was fixed in all SVN branches:

• Commit to main trunk:
  http://svn.apache.org/viewvc?view=rev&revision=682868
• Commit to 2.2 branch:
  http://svn.apache.org/viewvc?view=rev&revision=682870
• Commit to 2.0 branch:
  http://svn.apache.org/viewvc?view=rev&revision=682871

Upgrade to Apache HTTP Server 2.2.10 or 2.0.64 (as of August 6, these have not been released yet), or apply the patch from SVN commit r682868.

When Apache HTTP Server is configured with proxy support ("ProxyRequests On" in the configuration file), and when mod_proxy_ftp is enabled to support FTP-over-HTTP, requests containing wildcard characters (asterisk, tilde, opening square bracket, etc) such as:

GET ftp://host/*<foo> HTTP/1.0

lead to cross-site scripting in the response returned by mod_proxy_ftp:

[...]
<h2>Directory of <a href="/">ftp://host</a>/*<foo></h2>
[...]

To exploit this vulnerability, 'host' must be running an FTP server, and the last directory component of the path (the XSS payload) must be composed of at least 1 wildcard character and must not contain any forward slashes. In practice, this last requirement is not an obstacle at all to develop working exploits, example:

ftp://host/*<img%20src=""%20onerror="alert(42)">

Credit: Discovered by Marc Bevand of Rapid7.

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