---
id: CVE-2026-117556
title: zchunk before 1.5.5 Heap Out-of-Bounds Read via read_preface()
summary: >-
  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 f…
severity: medium
cvss: 4.3
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L'
cvssSource: cna
cwe:
  - CWE-125
vendor: zchunk
product: zchunk
affected:
  - zchunk < 1.5.5
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-10-28T15:54:22.919848Z'
published: '2026-10-27'
updated: '2026-10-28'
sourceUpdated: '2026-10-28T16:17:15.487Z'
source: CVEORG
sourceUrl: 'https://www.cve.org/CVERecord?id=CVE-2026-117556'
references:
  - url: 'https://github.com/zchunk/zchunk/issues/119'
    label: 'GitHub Issue #119'
  - url: 'https://github.com/zchunk/zchunk'
  - url: >-
      https://github.com/zchunk/zchunk/commit/02b371a64bf98245df97315d07c684a0ca5ea1df
  - url: 'https://github.com/zchunk/zchunk/releases/tag/1.5.5'
    label: zchunk 1.5.5 Release Notes
  - url: 'https://github.com/zchunk/zchunk/blob/1.5.4/src/lib/header.c#L167'
  - url: >-
      https://www.vulncheck.com/advisories/zchunk-before-1.5.5-heap-out-of-bounds-read-via-read-preface
    label: >-
      VulnCheck Advisory: zchunk before 1.5.5 Heap Out-of-Bounds Read via
      read_preface()
tags:
  - cve.org
epss: 0.00328
epssPercentile: 0.2582
ingestedAt: '2026-10-27T16:11:59.334Z'
---

## Overview

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

- `zchunk < 1.5.5`

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.