CVE-2025-43859

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.
HTTP Request/Response Smuggling
ProviderTypeBase ScoreAtk. VectorAtk. ComplexityPriv. RequiredVector
NISTNIST
9.1 CRITICAL
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
GitHub_MCNA
9.1 CRITICAL
NETWORK
LOW
NONE
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CISA-ADPADP
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Awaiting analysis
This vulnerability is currently awaiting analysis.
Base Score
CVSS 3.x
EPSS Score
Percentile: 13%
Ubuntu logo
Ubuntu Releases
Ubuntu Product
Codename
python-h11
plucky
Fixed 0.14.0-1ubuntu0.25.04.1
released
oracular
Fixed 0.14.0-1ubuntu0.24.10.1
released
noble
Fixed 0.14.0-1ubuntu0.24.04.1
released
jammy
not-affected
focal
not-affected
Common Weakness Enumeration
Vulnerability Media Exposure
References
https://github.com/python-hyper/h11/commit/114803a29ce50116dc47951c690ad4892b1a36ed
https://github.com/python-hyper/h11/security/advisories/GHSA-vqfr-h8mv-ghfj