CVE-2026-55367
Publication date 5 November 2026
Last updated 5 November 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| h2o | 26.10 stonking | Not in release |
| 26.04 LTS resolute | Not in release | |
| 24.04 LTS noble |
Needs evaluation
|
|
| 22.04 LTS jammy |
Needs evaluation
|
|
| 20.04 LTS focal |
Needs evaluation
|
|
| 18.04 LTS bionic |
Needs evaluation
|
|
| dnsdist | 26.10 stonking |
Not affected
|
| 26.04 LTS resolute |
Not affected
|
|
| 24.04 LTS noble |
Needs evaluation
|
|
| 22.04 LTS jammy |
Not affected
|
|
| 20.04 LTS focal |
Not affected
|
|
| 18.04 LTS bionic |
Not affected
|
|
| 16.04 LTS xenial |
Not affected
|
Notes
hlibk
Before dnsdist version 1.8.2-2, dnsdist used system h2o. Between 1.8.2-2 and 1.9.0, dnsdist vendored h2o. After 1.9.0, dnsdist switched from using h2o to nghttp2 and now uses system nghttp2. Also, before 1.4.0 dns-over-https support was not implemented.
Severity score breakdown
CVSS version: CVSS v3.0
Base score
7.5 · High
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H