Description
h2 is a pure-Python implementation of a HTTP/2 protocol stack. Prior to version 4.3.0, an HTTP/2 request splitting vulnerability allows attackers to perform request smuggling attacks by injecting CRLF characters into headers. This occurs when servers downgrade HTTP/2 requests to HTTP/1.1 without properly validating header names/values, enabling attackers to manipulate request boundaries and bypass security controls. This issue has been patched in version 4.3.0.
References (3)
Core 3
Core References
Vendor Advisory x_refsource_confirm
https://github.com/python-hyper/h2/security/advisories/GHSA-847f-9342-265h
Patch x_refsource_misc
https://github.com/python-hyper/h2/commit/035e9899f95e3709af098f578bfc3cd302298e3a
Scores
CVSS v4
6.9
EPSS
0.0171
EPSS Percentile
75.1%
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
CISA SSVC
Vulnrichment
Exploitation
none
Automatable
yes
Technical Impact
partial
Details
CWE
CWE-93
Status
published
Products (2)
pypi/h2
0 - 4.3.0PyPI
python-hyper/h2
< 4.3.0
Published
Aug 25, 2025
Tracked Since
Feb 18, 2026