Improper escaping of the redirection page (retrieved from the request's Referer header) allows an attacker to inject HTML.
While this is generally not directly actionable as modern browsers will URL-encode special characters, on some specific server configurations this could poison the cache, leading to cross-site scripting.
Impact
Cross-site scripting (XSS).
Patches
b1ebc57763f104eb5f541b7b4d1ce6948168abd9
Workarounds
None
Credits
Thanks to siunam (Tang Cheuk Hei) for discovering and responsibly reporting the issue.