CVE-2026-54522: Msgpack Messagepack

Medium severity, CVSS 5.4. EPSS: 0.2% chance of exploitation in the next 30 days.

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.

Affected products

• Msgpack Messagepack: before 1.8.2 (fixed in 1.8.2)

Published 2026-07-30. Last modified 2026-08-05.