Is CVE-2025-43859 in the CISA KEV catalog?

No. CVE-2025-43859 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2025-43859?

CVE-2025-43859 has a CVSS v3 base score of 9.1 (CRITICAL).

What is the EPSS score for CVE-2025-43859?

CVE-2025-43859 has an EPSS score of 0.52% (40th percentile), estimating the probability of exploitation in the next 30 days.

CVE & CISA-KEV Catalog

CVE-2025-43859

CRITICAL

9.1

CVSS v3

NVD

Description

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.

CWE-444

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploit Intelligence

0.52%probability of exploitation in 30 days

40thpercentile

Moderate risk: more likely to be exploited than 40% 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 2025-04-29.