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Vulnerabilities

Vulnerability · CVE-2026-21452

MessagePack for Java is a serializer implementation for Java.

Published Jan 2, 2026 · catalog updated Jan 2, 2026 · MessagePack for Java is

Last checked Nov 3, 2026. A connected source was read within the last 7 days.

Check if you run it

No confirmed exploitation is on record for CVE-2026-21452. EPSS is 0.60%. Act only if a listed version of MessagePack for Java is is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (MessagePack for Java is).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.60%
Remediation
Version ranges on file
Affected products
vendor msgpack msgpack-java < 0.9.11

MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getData() is invoked, the library attempts to allocate a byte array of the declared length without enforcing any upper bound. A malicious .msgpack file of only a few bytes can therefore trigger unbounded h

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • vendor msgpack msgpack-java < 0.9.11< 0.9.11

How to fix CVE-2026-21452

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-21452. EPSS is 0.60%. Act only if a listed version of MessagePack for Java is is installed.

Which versions are affected?

Compare what you have installed with msgpack msgpack-java < 0.9.11 < 0.9.11. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

No weakness class is stored. EPSS 0.60%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Jan 2, 2026 · EUVD

    Detected

    MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getDa

  2. Jan 2, 2026 · EUVD

    Updated

    MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers lazily, it later trusts the declared EXT payload length when materializing the extension data. When ExtensionValue.getDa

Sources

  • CVE.orgVulnerability recordCVE-2026-21452

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-21452

    30-day exploitation probability 0.60%

    first.org
  • EUVDVulnerability recordEUVD-2026-0750

    MessagePack for Java is a serializer implementation for Java. A denial-of-service vulnerability exists in versions prior to 0.9.11 when deserializing .msgpack files containing EXT32 objects with attacker-controlled payload lengths. While MessagePack-Java parses extension headers

    euvd.enisa.europa.eu

References

Freshness

Last verified in this catalog Nov 3, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.

  • FIRST EPSSNov 3, 2026
  • CVE.orgOct 31, 2026
  • EUVDOct 31, 2026