SSRF defense-in-depth: `urllib.request.urlopen` follows redirects by default,
so a probe at `http://example.com/v1/models` could be redirected to
`http://internal-service:8080/admin` — surfacing internal HTTP services to
the authenticated user. The probe is already gated behind WebUI auth and the
local-network check, so the practical attack surface is 'authenticated user
enumerating internal services' (same as `curl` from their browser DevTools).
Tightening the redirect default is cheap insurance.
Implementation:
- New module-level `_NoRedirectHandler` (subclasses `urllib.request.HTTPRedirectHandler`,
overrides `redirect_request` to return None — urllib then raises `HTTPError(3xx)`
rather than following).
- New module-level `_PROBE_OPENER = urllib.request.build_opener(_NoRedirectHandler())`.
- `probe_provider_endpoint` switches from `urlopen(req, …)` to `_PROBE_OPENER.open(req, …)`.
- The existing `HTTPError` handler now categorizes 3xx as `unreachable` with a
detail string mentioning 'redirect' so the user understands what happened.
3xx does NOT get its own error code in `PROBE_ERROR_CODES` — the error
taxonomy contract stays the same shape (frontend i18n unchanged).
Added regression test `test_probe_does_not_follow_redirects` in
`tests/test_issue1499_onboarding_probe.py`. Spins up a tiny HTTP server that
302-redirects `/v1/models` to `/different-endpoint` (which would return
`{'data': [{'id': 'should-not-see'}]}` if followed). Asserts the probe
returns `{ok: False, error: 'unreachable', status: 302, detail: …'redirect'…}`
and that the 'should-not-see' string never appears in the result.
Mutation-verified: reverting `_PROBE_OPENER.open` back to `urlopen` causes
the test to fail with "Probe followed a redirect — should have refused".
Suite delta: 3917 → 3918 passing (+1).
Reviewer-flagged in PR #1501. Per the
'reviewer-flagged-fix-in-release-not-followup' policy: <20 LOC defensive
fix, regression test path obvious, ship in this release rather than punting.
ba6f34488e