chunked: reject nul byte in trailer#21896
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Since verify_header does more checks than so, shouldn't it rather just call that function? |
Trailers are delivered to the application as headers via CLIENTWRITE_TRAILER, but unlike regular response headers they skipped the verify_header() checks, so a server could smuggle a nul byte (or stray CR) into a header reaching CURLOPT_HEADERFUNCTION and curl_easy_header(). Run each assembled trailer line through Curl_verify_header(), the same validation used for normal headers. Covered by the new test 2106.
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Good point. Exposed |
bagder
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Thanks! |
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Trailers are delivered to the application as headers via CLIENTWRITE_TRAILER, but unlike regular response headers they skipped the verify_header() checks, so a server could smuggle a nul byte (or stray CR) into a header reaching CURLOPT_HEADERFUNCTION and curl_easy_header(). Run each assembled trailer line through Curl_verify_header(), the same validation used for normal headers. Covered by the new test 2106. Closes curl#21896
dkarpov1970
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Jun 10, 2026
Trailers are delivered to the application as headers via CLIENTWRITE_TRAILER, but unlike regular response headers they skipped the verify_header() checks, so a server could smuggle a nul byte (or stray CR) into a header reaching CURLOPT_HEADERFUNCTION and curl_easy_header(). Run each assembled trailer line through Curl_verify_header(), the same validation used for normal headers. Covered by the new test 2106. Closes curl#21896
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Repro: fetch a chunked HTTP/1 response whose trailer line carries a nul byte, e.g.
chunky-trailer: he\0llo. curl currently accepts it and exits0.Cause:
httpchunk_readwrite()accumulates trailer bytes and forwards them to the client as headers (CLIENTWRITE_TRAILER), so the trailer reaches theCURLOPT_HEADERFUNCTIONcallback andcurl_easy_header(). Regular response headers run throughverify_header(), which rejects an embedded nul, but trailers never do, so a server can smuggle a nul into a header delivered to the application.Fix: reject a nul byte in the trailer parser, matching the
verify_header()behaviour for normal headers.Covered by the new test
2106.