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[3.12] gh-150743: Limit trailer lines and interim responses read by http.client (GH-150749)#152527

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[3.12] gh-150743: Limit trailer lines and interim responses read by http.client (GH-150749)#152527
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@miss-islington miss-islington commented Jun 28, 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.
(cherry picked from commit 84badb7)

Co-authored-by: Gregory P. Smith 68491+gpshead@users.noreply.github.com


This issue was reported to us via GHSA-w4q2-g22w-6fr4

…d by http.client (pythonGH-150749)

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 pythongh-88188 for CVE-2021-3737, which bounded header lines
within an interim response but not these two sibling loops.
(cherry picked from commit 84badb77f5bb26e51d9a5c478d0e3bfe7ab6eb6f)

Co-authored-by: Gregory P. Smith <68491+gpshead@users.noreply.github.com>

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This issue was reported to us via [GHSA-w4q2-g22w-6fr4](https://github.com/python/cpython/security/advisories/GHSA-w4q2-g22w-6fr4)
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