Vulnerability in Nghttp2

CVE-2026-27135

nghttp2 is an implementation of the Hypertext Transfer Protocol version 2 in C. Prior to version 1.68.1, the nghttp2 library stops reading the incoming data when user facing public API `nghttp2_session_terminate_session` or `nghttp2_session_terminate_session2` is called by the application. They might be called internally by the library when it detects the situation that is subject to connection error. Due to the missing internal state validation, the library keeps reading the rest of the data after one of those APIs is called. Then receiving a malformed frame that causes FRAME_SIZE_ERROR causes assertion failure. nghttp2 v1.68.1 adds missing state validation to avoid assertion failure. No known workarounds are available.

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.009 (57.8th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 58th percentile — 57.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-27135: held from 0.008 to 0.009.

EPSS over last 30 days · oldest: 0.008 · newest: 0.009 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-27135?
CVE-2026-27135 is a high-severity vulnerability in Nghttp2, classified under Reachable Assertion. CVSS score: 7.5/10. Published 2026-03-18.
How severe is CVE-2026-27135?
High severity. CVSS v3 base score is 7.5 out of 10.