CVE-2026-54522 describes a use-after-free vulnerability (CWE-416) in the msgpack-ruby library's Buffer#clear method prior to version 1.8.2. The problem arises because the internal pointers rmem_last, rmem_end, and rmem_owner are not properly cleared after _msgpack_buffer_shift_chunk returns a memory page to the shared pool. This stale state allows subsequent Buffer#write operations and other Buffer instances to alias the freed memory page, potentially leading to disclosure or corruption of data across buffers. The vulnerability has a low CVSS score of 2.1 and is fixed in msgpack-ruby version 1.8.2.

The vulnerability can cause cross-buffer data disclosure or corruption due to use-after-free conditions in memory management within msgpack-ruby buffers. The impact is limited to local scenarios (attack vector: local) with low complexity and requires partial attack techniques. There is no indication of remote exploitation or privilege escalation. No known exploits are reported in the wild.

Upgrade msgpack-ruby to version 1.8.2 or later where this use-after-free vulnerability is fixed. Since the vendor advisory confirms the fix in 1.8.2, applying this official update is the recommended remediation. No additional mitigations are specified.