Vulnerability · Published Oct 27, 2026 · Assigned by VulnCheck
CVE-2026-117556zchunk before 1.5.5 Heap Out-of-Bounds Read via read_preface()
Medium 4.3
In plain English
A medium-severity out-of-bounds read in zchunk from zchunk. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 26% of all known vulnerabilities).
Severity (CVSS 3.1)4.3Medium
Exploit odds (30 days)0.3%top 74.0% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known
Official description
zchunk before 1.5.5 contains a heap out-of-bounds read vulnerability in read_preface() in src/lib/header.c that passes the total header length instead of remaining bytes to compint parsing functions. Attackers can supply a crafted .zck file whose header ends inside a compressed integer, causing reads past the heap header buffer and crashing the application.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | zchunk | no fix listed | DEBIAN-CVE-2026-117556 |
| Debian:13 | zchunk | no fix listed | DEBIAN-CVE-2026-117556 |
| Debian:14 | zchunk | no fix listed | DEBIAN-CVE-2026-117556 |
| Ubuntu:22.04:LTS | zchunk | no fix listed | UBUNTU-CVE-2026-117556 |
| Ubuntu:24.04:LTS | zchunk | no fix listed | UBUNTU-CVE-2026-117556 |
| Ubuntu:26.04:LTS | zchunk | no fix listed | UBUNTU-CVE-2026-117556 |
| Ubuntu:26.10 | zchunk | no fix listed | UBUNTU-CVE-2026-117556 |
Affected products (as reported)
Weakness: CWE-125 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L
References
- GitHub Issue #119 issue-tracking
- https://github.com/zchunk/zchunk product
- https://github.com/zchunk/zchunk/commit/02b371a64bf98245df97315d07c684a0ca5ea1df patch
- zchunk 1.5.5 Release Notes release-notes
- https://github.com/zchunk/zchunk/blob/1.5.4/src/lib/header.c#L167 technical-description
- VulnCheck Advisory: zchunk before 1.5.5 Heap Out-of-Bounds Read via read_preface() third-party-advisory