fix: omit SSE CORS Origin values containing CR/LF/NUL - #52
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SSE reflected request Origin into Access-Control-Allow-Origin without the custom-header CTL filter from #50. Default MCP-style http://host:* allowlists still match after an embedded CR, enabling response header injection. Gate-deny custom headers now use the same writer. Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
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July 28, 2026 06:39
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Bug and impact
SSE CORS reflected the request
OriginintoAccess-Control-Allow-Originwithout the custom-header CTL filter from #50. With default MCP-stylehttp://host:*allowlists, an Origin likehttp://127.0.0.1:PORT\rX-Evil: 1still matches after the port colon, so the CR is written onto the response wire (header injection).Root cause
The SSE takeover path writes ACAO directly to the stream instead of going through
write_custom_response_headers. Port-wildcard Origin matching only checksprefix+:, so embedded CR/NUL after the port is accepted.Fix
is_unsafe_response_header).write_custom_response_headers(same filter as normal responses).Validation
NET_DISABLE_NETWORK_TESTS=0 tools/CB.sh debug test— new SSE CORS scenario passes; suite 609/609 tests passed (4 unrelated flaky assertions in posix/socket timeout tests).