Anubis vulnerable to possible XSS via redir parameter when using subrequest auth mode
Summary
When using subrequest authentication, Anubis did not perform validation of the redirect URL and redirects user to any URL scheme. While most modern browsers do not allow a redirect to javascript: URLs, it could still trigger dangerous behavior in some cases.
GET https://example.com/.within.website/?redir=javascript:alert() responds with Location: javascript:alert().
Impact
Anybody with a subrequest authentication seems affected. Using javascript: URLs will probably be blocked by most modern browsers, but using custom protocols for third-party applications might still trigger dangerous operations.
Note
This was originally reported by @mbiesiad against Weblate.
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