Prevent FastAPI login handler from redirecting off site#12742
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mekarpeles merged 3 commits intoMay 14, 2026
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Pull request overview
Patches an open-redirect vulnerability (GHSA-22xr-xvw5-m2r9) in the FastAPI login handler by validating the post-login redirect value, and hardens the session cookie attributes.
Changes:
- Adds
_safe_redirect()helper that rejects URLs with a scheme, netloc, leading//, or that don't begin with/, falling back to/. - Uses the helper for the
Locationheader on successful login. - Sets the session cookie with
secure=Trueandsamesite="lax"(wassecure=False, no SameSite).
Co-authored-by: Copilot Autofix powered by AI <[email protected]>
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The redirect form field was passed directly into the Location header with no validation, allowing open redirect to arbitrary external URLs.
_safe_redirect() now rejects any URL with a scheme, netloc, or leading // — falling back to /. Same-origin paths pass through unchanged.
Also fixes secure=False on the session cookie (authn-011) and adds SameSite=lax to match security best practices.
Addresses GHSA-22xr-xvw5-m2r9
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