CVE & CISA-KEV Catalog

CVE-2025-57804

UNSCOREDEPSS 73th pctl
NVD

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.

CWE-93

How to fix

Remediation Available
python-h2Debian
Fixed in:4.0.0-3+deb11u1CVE-2025-57804
Fixed in:4.3.0-1CVE-2025-57804

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3.1 Vector

No CVSS vector data available.

Exploit Intelligence

1.61%probability of exploitation in 30 days
73rdpercentile

Elevated risk: more likely to be exploited than 73% of all known CVEs.

References

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-11-03.