Best Practical reports:

We have determined a number of security vulnerabilities in commonly installed RT extensions, enumerated below. You can determine which, if any, of these extensions your RT installation is using by navigating to Configuration → Tools → System Configuration, and examining the "Plugins" configuration setting.

We have released updated versions of each vulnerable extension. Installation instructions for each are included in a README file in each extension's tarball. You need only download and upgrade these extensions if you have a previous version of them installed; RT installations with none of the below extensions installed are not vulnerable, and do not need to take action.

RT::Authen::ExternalAuth 0.10 and below (for all versions of RT) are vulnerable to an escalation of privilege attack where the URL of a RSS feed of the user can be used to acquire a fully logged-in session as that user. CVE-2012-2770 has been assigned to this vulnerability.

Users of RT 3.8.2 and above should upgrade to RT::Authen::ExternalAuth 0.11, which resolves this vulnerability. Because users of RT 3.8.1 cannot run RT::Authen::ExternalAuth later then 0.08 (due to bugs in plugin handling code in RT 3.8.1), we are also providing a patch which applies to RT::Authen::ExternalAuth 0.08. This patch should only be applied if you are running RT 3.8.1 and RT::Authen::ExternalAuth 0.08. Instructions for applying the patch can be found in the patch file itself.

References:
http://blog.bestpractical.com/2012/07/security-vulnerabilities-in-three-commonly-deployed-rt-extensions.html
http://cpan.metacpan.org/authors/id/A/AL/ALEXMV/RT-Authen-ExternalAuth-0.11.tar.gz
http://download.bestpractical.com/pub/rt/release/rt-authen-externalauth-0.08.patch