A vulnerable extension is one that has been found to contain (or contribute to) a security vulnerability.

Vulnerable extensions are not necessarily poorly-coded. As the Web evolves, technical requirements and commonly accepted coding practices change. Active projects release new versions of their extensions as requirements change. For this reason, it is important to:

1. Know the version numbers of all installed extensions.
2. Use only the latest stable version of all extensions.
3. Completely remove all files of insecure or unused extensions.
4. Check the Vulnerable Extension List on a regular basis and remove or update any extension version found to be vulnerable.