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Advisory record · GHSA-259r-337f-4rfw

Compress/s2: Integer Overflow or Wraparound and Out-of-bounds Write in compress

CVSS 7.5 HighEPSS 0.0057 · 47th percentile

Published by the GitHub Advisory Database at 20 Oct 2026, 14:33 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
github.com/klauspost/compressGo<1.18.71.18.7
Identifiers
GHSA-259r-337f-4rfw · CVE-2026-63209 · GO-2026-5841
Weakness (CWE)
CWE-190 · CWE-787
Tags
Published
20 Oct 2026
Updated
20 Oct 2026

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

A signed integer overflow in the Go package github.com/klauspost/compress (the s2 dictionary code, versions up to and including 1.18.6) lets a dictionary supplied to s2.NewDict bypass its repeat-index check. An attacker who can supply dictionary data to an application that later calls Dict.Encode can crash the process with an out-of-bounds memory access. Upgrade to version 1.18.7.

Written 1 Nov 2026.

Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

Severity and exploitation

ScoreRatingCVSSVectorSource
7.5 High 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H CNA (GitHub_M)
  • CISA KEV Not listed.
  • EPSS 0.0057, the 47th percentile, on 7 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:11 UTC First seen by agentprime
  2. 31 Oct 2026, 14:11 UTC Confirmed by OSV

Sources

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.