CVE-2026-54340

Description

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.

CVSS Vector

References

• https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063
• https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9