MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.7, the Java-platform msgpack gem for JRuby allocated arrays and byte buffers directly from attacker-controlled array32, str32, and bin32 declared sizes before confirming that corresponding elements or bytes were available. A short MessagePack header could therefore trigger a very large allocation or sustained heap growth when an application decoded untrusted input through MessagePack.unpack or MessagePack::Unpacker, potentially exhausting the shared JVM heap. map32 and declared counts at or above 2^31 did not use the affected allocation behavior. This issue is fixed in version 1.8.7.

No CVSS v4.0

Attack Vector Network

Attack Complexity Low

Privileges Required None

Scope Unchanged

Confidentiality Impact None

Integrity Impact None

Availability Impact High

User Interaction None

No CVSS v3.0

No CVSS v2

This CVE is not in the KEV list.

No EPSS score available.

Key SSVC decision points have not yet been added.

Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).

Vendor Product Default status Versions
msgpack msgpack-ruby affected
Version Status Constraints
< 1.8.7 affected —

No data.

No data.

No data.

Project Subscriptions

No data.

Advisories

No advisories yet.

Fixes

Solution

No solution given by the vendor.

Workaround

No workaround given by the vendor.

References
Link Providers
https://github.com/msgpack/msgpack-ruby/commit/ca0efc1256c687b428c46dd68ce000ff515d53f2 cve-icon
https://github.com/msgpack/msgpack-ruby/releases/tag/v1.8.6 cve-icon
https://github.com/msgpack/msgpack-ruby/releases/tag/v1.8.7 cve-icon
https://github.com/msgpack/msgpack-ruby/security/advisories/GHSA-73v3-wf97-vpgj cve-icon
History

Thu, 12 Nov 2026 22:45:00 +0000

Type Values Removed Values Added
Description MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.7, the Java-platform msgpack gem for JRuby allocated arrays and byte buffers directly from attacker-controlled array32, str32, and bin32 declared sizes before confirming that corresponding elements or bytes were available. A short MessagePack header could therefore trigger a very large allocation or sustained heap growth when an application decoded untrusted input through MessagePack.unpack or MessagePack::Unpacker, potentially exhausting the shared JVM heap. map32 and declared counts at or above 2^31 did not use the affected allocation behavior. This issue is fixed in version 1.8.7.
Title msgpack-java JRuby decoder allocates from declared header counts with no cap: 5-byte message forces multi-GiB OOM
Weaknesses CWE-1325
CWE-770
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'}

Projects

Sign in to view the affected projects.

cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-11-12T22:41:38.409Z

Reserved: 2026-11-10T21:12:01.228Z

Link: CVE-2026-126366

cve-icon Vulnrichment

No data.

cve-icon NVD

No data.

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses