Official MCP Registry v1.8.1 blocks github.io domains after an organization namespace takeover path

The official MCP Registry released v1.8.1 on 2026-08-06, blocking github.io domains in the DNS and HTTP token-exchange paths used to verify namespace ownership.

The registry grants publish rights two ways. The GitHub token method grants rights over io.github.<org>/* to organization owners only. The DNS and HTTP methods grant rights over a reversed domain to anyone who can prove control of that domain, and before this release neither method special-cased github.io or carried a blocked-domain list. Because GitHub Pages serves arbitrary files from an organization repository at <org>.github.io, anyone with write access to that repository could serve an auth key at /.well-known/mcp-registry-auth, exchange it for a token, and publish under the organization's namespace, bypassing the owner-only restriction the GitHub token method enforces.

The fix was applied in ValidateDomainAndTimestamp, the function shared by both exchanges, rejecting github.io and its subdomains case-insensitively. The timeline was tight: the fix commit landed at 22:38:34Z, v1.8.1 was published at 23:35:18Z, and production was promoted to 1.8.1 at 23:43:14Z, about 65 minutes end to end.

No CVE was assigned and no GitHub Security Advisory was published. The registry repository's advisories page lists five records, the newest dated 2026-05-12, none covering this issue. The only public account is the pull request and the release notes.