PT-2026-60605 · H2O · H2O

CVE-2026-54340 · Published 2026-07-16 · Updated 2026-07-17

NVD

CVSS v3.1

7.5

High

Base vector

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

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.

Fix

Allocation of Resources Without Limits

Resource Exhaustion

Weakness Enumeration

CWE-770

CWE-400

Related Identifiers

CVE-2026-54340

Affected Products

H2O

References · 3

• https://nvd.nist.gov/vuln/detail/CVE-2026-54340 · Security Note
• https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9 · Note
• https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063 · Note