CVE-2026-54340

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 v3 7.5 HIGH

7.5^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 3.6

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact NONE

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://github.com/h2o/h2o/commit/9265bdd9a996ed992681055e3996baf3e09d2063	Patch
https://github.com/h2o/h2o/security/advisories/GHSA-qcrr-wrhc-pgq9	Third Party Advisory

Configurations

Configuration 1 (hide)

cpe:2.3:a:h2o:h2o:*:*:*:*:*:*:*:*

History

No history.

Information

Published : 2026-07-17 00:16

Updated : 2026-08-05 19:47

NVD link : CVE-2026-54340

Mitre link : CVE-2026-54340

CVE.ORG link : CVE-2026-54340

JSON object : View

Products Affected

h2o

h2o

CWE

CWE-400

Uncontrolled Resource Consumption

CWE-770

Allocation of Resources Without Limits or Throttling

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