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Advisory record · GHSA-cw39-r4h6-8j3x

MessagePack for Java Vulnerable to Remote DoS via Malicious EXT Payload Allocation

CVSS 7.5 HighEPSS 0.0060 · 49th percentile

Published by the GitHub Advisory Database at 5 Jan 2026, 14:59 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

PackageEcosystemAffectedFixed in
org.msgpack:msgpack-coreMaven<0.9.110.9.11
Identifiers
GHSA-cw39-r4h6-8j3x · CVE-2026-21452
Weakness (CWE)
CWE-400 · CWE-789
Tags
Published
5 Jan 2026
Updated
10 Sept 2026

Machine-written summary

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

MessagePack for Java (org.msgpack:msgpack-core) versions before 0.9.11 are vulnerable to a denial of service when deserializing a crafted .msgpack file containing an EXT32 object with an excessively large declared payload length. An attacker who can supply such a file, for example to a service that loads untrusted model files, can cause the JVM to allocate unbounded memory and crash or become unavailable. Upgrade to msgpack-core 0.9.11, which allocates memory gradually for large inputs. No workaround is given in the source.

Written 2 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 0.0060, the 49th percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

  1. 31 Oct 2026, 14:17 UTC First seen by agentprime
  2. 31 Oct 2026, 14:17 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.