Vulnerability record · CVE-2026-54522 · published 30 July 2026

CVE-2026-54522: Msgpack messagepack use after free vulnerability

Msgpack · Messagepack

MessagePack for Ruby is an implementation of the MessagePack binary serialization format. Prior to 1.8.2, MessagePack::Buffer#clear in ext/msgpack/buffer.c leaves rmem_last, rmem_end, and rmem_owner stale after _msgpack_buffer_shift_chunk returns an rmem page to the shared pool, allowing a subsequent Buffer#write and a second MessagePack::Buffer to alias the page and disclose or corrupt cross-buffer data. This issue is fixed in version 1.8.2.

2.1 CVSS 4.0 Low EPSS 0.23% · top 87.9% CWE-416 · Use after free

2.1CVSS 4.0 base score

0.23%EPSS exploitation probability, 30 days

NoNot in CISA KEV

1Affected product versions listed by NVD

3References, 2 tagged exploit

5 Aug 2026Last modified by NVD

Description

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

Messagepack Msgpack

References

Link	Tags
https://github.com/msgpack/msgpack-ruby/commit/5627d71606b565641d2dd501b82aae862f4abe90	Patch
https://github.com/msgpack/msgpack-ruby/security/advisories/GHSA-4mrv-5p47-p938	ExploitVendor Advisory
https://github.com/msgpack/msgpack-ruby/security/advisories/GHSA-4mrv-5p47-p938	ExploitVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-54522), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.