CVE-2011-3368: Input Validation

RMDG partner and independent security consultancy, "Context Information Security" has made CPNI Response aware of a security vulnerability which could potentially allow an attacker to gain full internal access to a network from the internet.

The technique exploits insecurely configured reverse web proxies to gain access to internal/DMZ systems.

This attack is based on an Apache web server which is using "modrewrite" to proxy web requests internally. Other proxies may suffer from this issue.

The vulnerability occurs if the Apache configuration file is configured like this:

RewriteRule ^(.) http://internalserver:80$1 [P]

As opposed to:

RewriteRule ^(.) http://internalserver:80/$1 [P]

It is important for readers to review their reverse proxy configurations to ensure that the rewrite rules are securely configured and cannot be abused in such a way that they can be used to compromise internal systems.