gh-150743: Limit trailer lines and interim responses read by http.client#150741
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gh-150743: Limit trailer lines and interim responses read by http.client#150741gpshead wants to merge 4 commits into
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A server could stream syntactically valid trailer lines forever after the final chunk of a chunked response, so reading the response would never return. Socket timeouts cannot interrupt this because data keeps arriving within every timeout window. Trailer lines are now counted against the same limit as response headers (max_response_headers, 100 by default) and HTTPException is raised when the limit is exceeded.
HTTPResponse.begin() skipped 100 Continue responses in an unbounded loop, so a server streaming them forever would hang getresponse() regardless of any socket timeout. At most 100 interim responses are now skipped before HTTPException is raised.
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needs backport to 3.10
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3.14 and earlier backport in #150749 |
sethmlarson
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Jun 2, 2026
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http.client read chunked-response trailer lines and skipped interim (1xx)
responses in unbounded loops, so a server streaming either forever would
hang the client even with a socket timeout set (data keeps arriving, so
the timeout never fires).
Trailer lines are now limited to max_response_headers (100 by default)
and interim responses to 100; HTTPException is raised past either limit.
Follow-up to gh-88188 for CVE-2021-3737, which bounded header lines
within an interim response but not these two sibling loops.
This issue was reported to us via GHSA-w4q2-g22w-6fr4 and was determined not to be high enough severity to handle privately.