fix: use exact match for loopback hosts in issuer URL validation#2089
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fix: use exact match for loopback hosts in issuer URL validation#2089
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validate_issuer_url() used startswith("127.0.0.1") to exempt loopback
addresses from the HTTPS requirement. This prefix match incorrectly
allowed non-loopback hostnames like 127.0.0.1.evil.com or
127.0.0.1something.example.com to bypass the HTTPS check.
Replace with an exact match against the set of loopback hosts
(localhost, 127.0.0.1, [::1]), consistent with the DNS rebinding
protection elsewhere in the codebase. This also adds the missing
IPv6 loopback (::1) exemption.
Remove pragma: no cover from validation branches now that they
have dedicated test coverage.
felixweinberger
approved these changes
Feb 18, 2026
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Problem
validate_issuer_url()usedstartswith("127.0.0.1")to exempt loopback addresses from the HTTPS requirement. This is a string prefix match, not an exact equality check, so it incorrectly allowed non-loopback hostnames like127.0.0.1.evil.comor127.0.0.1something.example.comto bypass the HTTPS check.Additionally, the IPv6 loopback address
::1was not covered by the exemption, despite being handled correctly in the DNS rebinding protection elsewhere in the codebase.Fix
Replace the
startswithprefix check with an exact match against the set of loopback hosts (localhost,127.0.0.1,[::1]), consistent with the approach used in the DNS rebinding auto-config inlowlevel/server.pyandmcpserver/server.py.Also removed
pragma: no coverfrom the validation branches now that they have dedicated test coverage.AI Disclaimer