[Laihu08]

Summary

_download_search_image fetched the reference-image URL with plain requests.get. That left two gaps in the allow-list: HTTP_PROXY/HTTPS_PROXY/ALL_PROXY made the request go through a proxy instead of the address that was checked, and 64:ff9b::/96 (NAT64) reports is_global == True, so 64:ff9b::7f00:1 mapped back to 127.0.0.1.

The fetch now uses build_guarded_session() (ignores ambient proxies, checks the connected peer) and _assert_url_host_allowed delegates to validate_download_url(), which blocks the NAT64 prefixes as reserved. The manual per-hop redirect loop and the 422 responses are unchanged.

Related Issues / Discussions

Closes #9633

QA Instructions

pytest tests/app/util/test_ssrf.py tests/app/routers/test_image_map.py
172 passed

The three new/updated tests in test_image_map.py (redirect re-validation through the guarded session, NAT64 literal and hostname rejected with 422 before any request, proxy env vars ignored) fail on main and pass with this change. ruff check and ruff format --check pass.

Review

Small change in one router; no API schema change.

Checklist

• The PR has a short but descriptive title, suitable for a changelog
• Meaningful regression coverage added / updated where needed; obsolete tests/code removed
• Persisted-state and API changes include required migrations / compatibility validation (none needed)
• Relevant performance/efficiency opportunities considered; material claims have evidence
• Material review findings resolved and relevant checks rerun
• Documentation added / updated (if applicable)
• Updated What's New copy (if doing a release after this PR)

AI assistance: this change was prepared with Claude (an AI coding assistant) and tested as described above.

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