by Kastro
Paper/Archive/CVE-2025-43859

CVE-2025-43859

python-hyper h11 — h11 accepts some malformed Chunked-Encoding bodies

EPSS 0.6%CVSS 9.1
critical.is priorityof 100
37
CVSS 9.1 (CNA)9.1 / 10 × 3027.3Not in CISA KEV+300.0EPSS percentile 48.4.484 × 209.7No public exploit+100.0SSVC exploitation: none+100.0
Description · from the CVE record

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

ProductAffectedFixed inSource
h11< 0.16.0–CNA

Scores by source

GitHub_M (CNA)9.1CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA ADPSSVCExploitation: none · Automatable: yes · Technical impact: total

References

refgithub.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfjrefgithub.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed