GHSA-j2pq-22jj-4pm5

### Impact
On instances where `Extension Repository Application` is installed, any user can execute any code requiring `programming` rights on the server.
In order to reproduce on an instance, as a normal user without `script` nor `programming` rights, go to your profile and add an object of type `ExtensionCode.ExtensionClass`. Set the description to `{{async}}{{groovy}}println("Hello from Description"){{/groovy}}{{/async}}` and press `Save and View`. If the description displays as `Hello from Description` without any error, then the instance is vulnerable.

### Patches
This vulnerability has been fixed in XWiki 15.10.9 and 16.3.0.

### Workarounds
Since `Extension Repository Application` is not mandatory, it can be safely disabled on instances that do not use it.
It is also possible to manually apply [this patch](https://github.com/xwiki/xwiki-platform/commit/8659f17d500522bf33595e402391592a35a162e8#diff-9b6f9e853f23d76611967737f8c4072ffceaba4c006ca5a5e65b66d988dc084a) to the page `ExtensionCode.ExtensionSheet`, as well as [this patch](https://github.com/xwiki/xwiki-platform/commit/8659f17d500522bf33595e402391592a35a162e8#diff-d571404d94fa27360cfee64f2a11d8c819b397529db275e005606b7356610f82) to the page `ExtensionCode.ExtensionAuthorsDisplayer`.

### References
* https://jira.xwiki.org/browse/XWIKI-21890
* https://github.com/xwiki/xwiki-platform/commit/8659f17d500522bf33595e402391592a35a162e8

### For more information

If you have any questions or comments about this advisory:
* Open an issue in [Jira XWiki.org](https://jira.xwiki.org/)
* Email us at [Security Mailing List](mailto:[email protected])