CVE-2026-44453
Publication date 17 July 2026
Last updated 17 July 2026
Ubuntu priority
Description
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling alloca. The maximum size of the memory allocated using alloca can be as huge as ~600KB, which exceeds the default pthread stack size used by musl libc (128KB). If the amount of memory allocated by alloca exceeds the stack size, the h2o server crashes with a segmentation fault, while it tries to touch the guard page. This issue has been fixed by commit 6b5370d.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| h2o | 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 | 26.04 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
|
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