CVE-2026-54340CWE-400CWE-770denial-of-service

CVE-2026-54340

High · published July 17, 2026

CVSS v3.1
7.5
EPSS
0%
Percentile
41.4
In the wild
Unconfirmed
What it is

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can be retained by stalled HTTP/2 streams, and depending on the configuration, additional limits are needed to bound decoded header state and prevent attack. This issue has been fixed by commit 9265bdd.

The record
Technical detail
CVSS v3.1
7.5 · HIGH
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
CVSS v4.0
Not supplied
EPSS
0.00493 · 41.4th percentile
Weaknesses
CWE-400 · Uncontrolled Resource Consumption; CWE-770 · Allocation of Resources Without Limits or Throttling
Published
2026-07-17T04:16Z
Affected products (1)
ProductVersionsFixed in
h2o/h2o≥ 2026-05-29, < 2026-06-042026-06-04
References (2)
https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063 · [email protected]https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9 · [email protected]
EPSS history
Timeline
  • 16 JUL 23:29Z
    h2o has HTTP/2 state amplification
    cvelistv5