GHSA-vh5c-jqfg-mhrh

### Impact
It's possible to know if a user has or not an account in a wiki related to an email address, and which username(s) is actually tight to that email by forging a request to the Forgot username page. Note that since this page does not have a CSRF check it's quite easy to perform a lot of those requests.

### Patches
This issue has been patched in XWiki 12.10.5 and 13.2RC1. Two different patches are provided:
- a first one to fix the CSRF problem
- a more complex one that now relies on sending an email for the Forgot username process.

### Workarounds
It's possible to fix the problem without uprading by editing the ForgotUsername page in version below 13.x, to use the following code: https://github.com/xwiki/xwiki-platform/blob/69548c0320cbd772540cf4668743e69f879812cf/xwiki-platform-core/xwiki-platform-administration/xwiki-platform-administration-ui/src/main/resources/XWiki/ForgotUsername.xml#L39-L123

In version after 13.x it's also possible to edit manually the forgotusername.vm file, but it's really encouraged to upgrade the version here.

### References
* https://jira.xwiki.org/browse/XWIKI-18384
* https://jira.xwiki.org/browse/XWIKI-18408

### For more information
If you have any questions or comments about this advisory:
* Open an issue in [Jira XWiki](https://jira.xwiki.org)
* Email us at [security ML](mailto:[email protected])