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)
Scores
CVSS v4
6.9
EPSS
0.0007
EPSS Percentile
21.7%
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
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