Dashboard / CVE-2026-55367

CVE-2026-55367

HIGH
MEDIUM Priority: 0.03 BB Relevance: 75/100
Published: 2026-11-04 Modified: 2026-11-12 First seen: 2026-11-04 Status: active

Attack Surface

Network Low Complexity No Auth No Interaction

CVSS Vector Breakdown

AV: Network
AC: Low
PR: None
UI: None
S: Unchanged
C: None
I: None
A: High

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.

Weakness Classification (1)

Affected Software (2)

VendorProductVersion
h2o h2o < 4212ce114506a073505fd389db16ad2ba4e582a0
h2o h2o < 4212ce114506a073505fd389db16ad2ba4e582a0

References & Advisories (3)

Bug Bounty Relevance

75 / 100
✓ Network accessible
✓ No authentication
✓ Low complexity
✓ No user interaction

CVSS Score

7.5 / 10.0 v3.1
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploitation Probability

0.34%
Raw Score 0.003390
Percentile 27.7%
Date 2026-11-14

EPSS Trend

2026-11-14
0.00339
2026-11-13
0.00339
2026-11-12
0.00339
2026-11-10
0.00339
2026-11-09
0.00339
2026-11-08
0.00339
2026-11-07
0.00339
2026-11-06
0.00339
2026-11-05
0.00339

Intelligence Sources

mitre ref →
nvd ref →

External Links