Use After Free in Msgpack Messagepack
CVE-2026-54522
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.
Vulnerability class: Use-After-Free
EPSS: 0.002 (5.9th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 5.4 (Medium). Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:L/A:N.
Affected products
- Msgpack Messagepack
- Msgpack Msgpack-ruby — versions < 1.8.2
Weakness classification (CWE)
References
- security-advisories@github.com (x_refsource_CONFIRM, Exploit, Vendor Advisory)
- security-advisories@github.com (Patch, x_refsource_MISC)
Frequently asked questions
- What is CVE-2026-54522?
- CVE-2026-54522 is a medium-severity vulnerability in Msgpack Messagepack, classified under Use After Free. CVSS score: 5.4/10. Published 2026-07-30.
- How severe is CVE-2026-54522?
- Medium severity. CVSS v3 base score is 5.4 out of 10.