CVE-2026-55367

EUVD-2026-117179

04.11.2026, 22:18

h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 4212ce114506a073505fd389db16ad2ba4e582a0, a client could send an incomplete CONNECT-UDP Capsule with an excessively large declared length, causing H2O to keep buffering received bytes without a per-Capsule limit while waiting for the remainder. Deployments that enabled proxy.connect-udp and accepted CONNECT-UDP requests could exhaust server memory and lose availability. This vulnerability is fixed with commit 4212ce114506a073505fd389db16ad2ba4e582a0.

Provider	Type	Base Score	Atk. Vector	Atk. Complexity	Priv. Required	Vector
NIST	Primary	7.5 HIGH	NETWORK	LOW	NONE	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Awaiting analysis

This vulnerability is currently awaiting analysis.

Base Score

CVSS 3.x

EPSS Score

Percentile: Unknown

Common Weakness Enumeration

CWE-770 - Allocation of Resources Without Limits or Throttling
The software allocates a reusable resource or group of resources on behalf of an actor without imposing any restrictions on the size or number of resources that can be allocated, in violation of the intended security policy for that actor.

References

https://github.com/h2o/h2o/commit/4212ce114506a073505fd389db16ad2ba4e582a0

https://github.com/h2o/h2o/pull/3754

https://github.com/h2o/h2o/security/advisories/GHSA-q342-qp8v-p44c