fix: omit framing and CR/LF custom headers from HTTP responses - #50
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http::server appended handler custom_headers after writing Content-Length and Connection. Echoing request Content-Length (copy-all headers) or values containing CR/LF/NUL produced duplicate framing or response splitting for proxies that prefer the last Content-Length. Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
http::server appended handler custom_headers after writing Content-Length and Connection. Echoing request Content-Length (copy-all headers) or values containing CR/LF/NUL produced duplicate framing or response splitting for proxies that prefer the last Content-Length. Also skip other hop-by-hop / framing-adjacent names (Upgrade, Keep-Alive, TE, Trailer(s), proxy-*). Co-authored-by: Cursor <cursoragent@cursor.com>
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Filter custom response headers for framing/hop-by-hop names and CR/LF/NUL before writing them after the server's Content-Length / Connection lines. Co-authored-by: Cursor <cursoragent@cursor.com>
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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: Cursor Agent <cursoragent@cursor.com> Co-authored-by: Kaius Ruokonen <ruoka@users.noreply.github.com>
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Summary
http::serverwrote handlercustom_headersafter its ownContent-Length/Connectionlines with no filtering (net-http_server.c++mresponse path).Trigger: A handler that copies request headers into the response (pattern exercised in middleware tests) receives a GET/POST with
Content-Length: 0(or any CL ≠ body size). The response then contains both the server'sContent-Length: <body>and a secondcontent-length: <request CL>.Impact: Proxies that prefer the last Content-Length desynchronize from the real body (HTTP response smuggling / cache desync). Values containing CR/LF/NUL in custom headers similarly enable response splitting (including CORS Origin bare-CR reflection when the origin validator allows it).
Fix
Before writing custom response headers, skip:
content-length,transfer-encoding,connectionSafe custom headers (e.g.
x-ok) are still emitted.Test plan
NET_DISABLE_NETWORK_TESTS=0 tools/CB.sh debug test— new scenarios pass (omit echoed CL; omit CR/LF values). Unrelated flakyconnect_with_timeout/socket::wait_forassertions may fail in this sandbox.