The TimThumb script is exploitable only if the WebShot feature is enabled. By default, WebShot is disabled.
TimThumb is a small php script for cropping, zooming and resizing web images (jpg, png, gif). Many WordPress themes and plugins distribute this script. A remote code execution vulnerability was reported in the WebShot feature of this script. This vulnerability was reported in v2.8.13 but previous versions are also vulnerable.
Upgrade to the latest version of timthumb or disable the WebShot feature (if enabled).