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Require a numeric port in wildcard Host/Origin matching - #1193
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Kehrlann merged 3 commits intoOct 20, 2026
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The wildcard-port patterns (e.g. "localhost:*") used a bare prefix match, so values like "localhost:evil.com" or "http://localhost:3000.evil.com" were accepted. Require a non-empty ASCII-digits-only port after the prefix.
Reject ports that are out of range (0, 65536) or longer than five digits, and use the same invalid-port cases for both Origin and Host. See modelcontextprotocol#1192 Signed-off-by: Daniel Garnier-Moiroux <git@garnier.wf>
Kehrlann
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October 20, 2026 11:27
Kehrlann
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Oct 20, 2026
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Fixes #1192
Motivation and Context
Wildcard-port patterns (
localhost:*,http://localhost:*) matched with a barestartsWith(base + ":"), so values like127.0.0.1:evil.com,localhost:@evil.comandhttp://localhost:3000.evil.comwere accepted. Browsers can't send these headers, so this is hardening and correctness rather than a standalone bypass. Related: modelcontextprotocol/python-sdk#3364. The Swift SDK already requires a digits-only port.What changed
After the prefix, the remainder must be a non-empty string of ASCII digits. The no-port form (
localhost) and exact matches are unchanged. No 1-65535 range check, matching Swift. One side effect: an Origin likehttp://localhost:8080/pathis now rejected; real Origin headers never include a path.How Has This Been Tested?
New parameterized tests for the Origin and Host wildcard cases (bad suffixes rejected,
127.0.0.1:8080andhttp://localhost:3000still accepted). Reverting the fix makes 16 of them fail. The whole mcp-core module passes (585 tests) with spring-javaformat validation. The Docker-based mcp-test integration tests weren't run locally.Types of changes
Checklist