---
id: "CVE-2026-117556"
kind: "vulnerability"
aliases: ["CVE-2026-117556"]
title: "zchunk: crafted .zck file triggers heap out-of-bounds read and crash"
severity: "medium"
cvss: 5.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["dnf", "linux-packaging", "package", "zchunk"]
not_affected_if: ["zchunk-1.5.5-or-later"]
published_at: "2026-10-27T14:16:36+00:00"
first_seen_at: "2026-10-27T14:32:19+00:00"
updated_at: "2026-10-27T14:33:10+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-117556", "first_seen_at": "2026-10-27T14:32:19+00:00"}]
---

# zchunk: crafted .zck file triggers heap out-of-bounds read and crash

zchunk before 1.5.5 passes the total header length instead of the remaining bytes to its compressed-integer parser in read_preface(). A crafted .zck file whose header ends mid-integer makes the parser read past the heap buffer, crashing the application.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Run `zck --version` or check the installed zchunk package version; versions below `1.5.5` are affected.
- unknown

## Fix

- Upgrade zchunk to `1.5.5` or later.

## Timeline

- 2026-10-27T14:32:19+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-117556

## From the sources

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.

---

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