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CVE PROGRAM SOURCE RECORD9.1 Critical

CVE-2025-43859

h11 accepts some malformed Chunked-Encoding bodies

Description

h11 is a Python implementation of HTTP/1.1. Prior to version 0.16.0, a leniency in h11's parsing of line terminators in chunked-coding message bodies can lead to request smuggling vulnerabilities under certain conditions. This issue has been patched in version 0.16.0. Since exploitation requires the combination of buggy h11 with a buggy (reverse) proxy, fixing either component is sufficient to mitigate this issue.

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

python-hyper h11

  • < 0.16.0affected

References