fix: don't DNS-resolve redirect_uris during client registration - #488
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masv3971 merged 2 commits intoJul 29, 2026
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The redirect_uri validator resolved hostnames via net.LookupIP() and rejected URIs whose hostnames didn't resolve (for http/https). This caused ccTLD domains like example.se to fail registration while example.org (which resolves to an IANA-reserved IP) succeeded. Redirect URIs are never fetched server-side — they're URLs the browser is redirected to. The SSRF concern that motivated the DNS check doesn't apply here. Remove the DNS resolution and private-IP blocking from the redirect_uri validator, keeping only the syntactic checks required by RFC 6749 (scheme present, no fragment). The safe_uri validator (used for server-side fetches like logo_uri) retains its DNS/SSRF checks. Add test cases for ccTLD and non-resolving hostnames.
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Pull request overview
This PR updates the OAuth/OIDC dynamic client registration validation logic to stop DNS-resolving redirect_uris during registration, aligning validation with the fact that redirect URIs are not fetched server-side and avoiding false rejections for non-resolving domains.
Changes:
- Removed DNS resolution and private-IP blocking from the
redirect_urivalidator. - Kept SSRF/DNS protections in
safe_uri(for server-fetched metadata URIs). - Added registration validation tests covering ccTLD and non-resolving hostnames.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| pkg/helpers/validate.go | Removes DNS/SSRF checks from redirect_uri validation logic and updates comments accordingly. |
| internal/verifier/apiv1/handler_client_registration_test.go | Adds test cases ensuring non-resolving redirect URI hostnames are accepted. |
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Native-app redirect URIs (e.g. com.example.app:/oauth2redirect) use custom schemes without an authority component. Only require a hostname for http/https schemes; for custom schemes, require at least a path or opaque component beyond the scheme.
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Fixes #487
Problem
The
redirect_urivalidator resolved hostnames vianet.LookupIP()and rejected URIs whose hostnames didn't resolve (for http/https). This caused ccTLD domains likeexample.seto fail registration whileexample.org(which resolves to an IANA-reserved IP) succeeded.Fix
Remove DNS resolution and private-IP blocking from the
redirect_urivalidator. Redirect URIs are never fetched server-side — they're URLs the browser is redirected to. The SSRF concern that motivated the DNS check doesn't apply.Keep only the syntactic checks required by RFC 6749 (scheme present, no fragment).
The
safe_urivalidator (used for server-side fetches likelogo_uri) retains its DNS/SSRF checks.Tests
Added test cases for ccTLD (
example.se) and non-resolving hostnames (nonexistent.test).