Both the Mac and Windows versions of Photoshop CS6 (aka Photoshop 13.0) contain a critical vulnerability that could allow an attacker to take control of affected systems.
An exploit for the buffer overflow vulnerability would require the user to be induced into opening a malicious file.
Since Photoshop has not been a traditional target for attackers, Adobe recommends administrators "install the update at their discretion" rather than as a matter of urgency.
That said, the Photoshop 13.0.1 update contains 75 other bug fixes, including 31 for problems known to cause crashes, 18 pertaining to 3D features, and 15 for drawing and graphics features.
The update can most conveniently be installed by selecting Updates from Photoshop's Help menu.
Earlier versions of Photoshop are not affected by the security issue.