Description
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.
Published: 2026-11-04
Score: 7.5 High
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

No vendor fix or workaround currently provided.

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Tracking

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History

Fri, 06 Nov 2026 19:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


Wed, 04 Nov 2026 23:00:00 +0000

Type Values Removed Values Added
First Time appeared H2o
H2o h2o
Vendors & Products H2o
H2o h2o

Wed, 04 Nov 2026 21:45:00 +0000

Type Values Removed Values Added
Description 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.
Title h2o: heap exhaustion using capsules
Weaknesses CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-11-05T20:01:20.480Z

Reserved: 2026-06-16T18:57:40.180Z

Link: CVE-2026-55367

cve-icon Vulnrichment

Updated: 2026-11-05T19:59:34.793Z

cve-icon NVD

Status : Received

Published: 2026-11-04T22:18:06.167

Modified: 2026-11-05T20:17:58.603

Link: CVE-2026-55367

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

Updated: 2026-11-04T23:00:21Z

Weaknesses