Steps to replicate the issue (include links if applicable):
- Install CheckUser
- Make a test edit using a user agent containing the character /303 which seems to be ä
- Run Special:CheckUser's 'get users' mode
What happens?:
The user agent is empty
What should have happened instead?:
The user agent should have been displayed
Software version (skip for WMF-hosted wikis like Wikipedia):
Producable on the English Wikipedia and on a local testing wiki
Other information (browser name/version, screenshots, etc.):
Cannot post the exact information as that is NDA covered.
Would suggest that CheckUser uses htmlspecialchars and unescaped definitions in the mustache file unless a fix can be easily found. This issue seems to be very rare but reduces the usefulness of the results.