---
id: CVE-2026-63209
title: compress provides various compression algorithms
summary: >-
  compress provides various compression algorithms. Prior to version 1.18.7, a
  signed integer overflow vulnerability in s2.NewDict() allows an attacker to
  bypass repeat index validation by supplying a dictionary with a
  uvarint-encoded repe…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-190
  - CWE-787
vendor: klauspost
product: compress
affected:
  - compress < 1.18.7
published: '2026-09-29'
updated: '2026-09-29'
sourceUpdated: '2026-09-29T17:17:08.843'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63209'
references:
  - url: >-
      https://github.com/klauspost/compress/commit/539243b8823ee8f03e49969823d57c348c917536
    label: security-advisories@github.com
  - url: 'https://github.com/klauspost/compress/releases/tag/v1.18.7'
    label: security-advisories@github.com
  - url: >-
      https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
    label: security-advisories@github.com
  - url: >-
      https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
tags:
  - nvd
  - cve.org
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-09-29T16:31:39.668233Z'
ingestedAt: '2026-09-29T16:39:33.260Z'
---

## Overview

compress provides various compression algorithms. Prior to version 1.18.7, a signed integer overflow vulnerability in s2.NewDict() allows an attacker to bypass repeat index validation by supplying a dictionary with a uvarint-encoded repeat value exceeding MaxInt64. When Dict.Encode() is subsequently called, the overflowed negative repeat value causes an out-of-bounds memory access via unsafe.Pointer arithmetic, crashing the process with SIGSEGV. This issue has been patched in version 1.18.7.

## Remediation

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