Vulnerability · Published Jul 30, 2026 · Assigned by GitHub_M
CVE-2026-54522MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure
Low 2.1
In plain English
A low-severity use-after-free in msgpack-ruby from msgpack. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 13% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | ruby-msgpack | no fix listed | DEBIAN-CVE-2026-54522 |
| Debian:13 | ruby-msgpack | no fix listed | DEBIAN-CVE-2026-54522 |
| Debian:14 | ruby-msgpack | 1.8.3-1 | DEBIAN-CVE-2026-54522 |
| RubyGems | msgpack | 1.8.2 | GHSA-4mrv-5p47-p938 |
| Ubuntu:22.04:LTS | ruby-msgpack | no fix listed | UBUNTU-CVE-2026-54522 |
| Ubuntu:24.04:LTS | ruby-msgpack | no fix listed | UBUNTU-CVE-2026-54522 |
| Ubuntu:26.04:LTS | ruby-msgpack | no fix listed | UBUNTU-CVE-2026-54522 |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| msgpack | msgpack-ruby | < 1.8.2 |
Weakness: CWE-416 · Vector: 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