CVE-2026-54340 – h2o has HTTP/2 state amplification

CVE ID :CVE-2026-54340

Published : July 17, 2026, 12:16 a.m. | 1 hour, 19 minutes ago

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.

Severity: 7.5 | HIGH

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