Chora is a PHP-based SVN/CVS repository viewer by the HORDE project.
A vulnerability in the diff viewer of Chora allows an attacker to inject shellcode. An attacker can exploit PHP's file upload functionality to upload a malicious binary to a vulnerable server, chmod it as executable, and run the file.
An attacker could remotely execute arbitrary binaries with the permissions of the PHP script, conceivably allowing further exploitation of local vulnerabilities and remote root access.
There is no known workaround at this time.
All users are advised to upgrade to the latest version of Chora:
# emerge sync
# emerge -pv ">=www-apps/horde-chora-1.2.2"
# emerge ">=www-apps/horde-chora-1.2.2"