MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure — GHSA-4MRV-5P47-P938

Summary

### Summary `MessagePack::Buffer#clear` shifts out every chunk and returns its 4 KiB rmem page to the shared pool, but does not reset the buffer's rmem cursor (`rmem_last`, `rmem_end`, `rmem_owner`). The next write sees "unused rmem space" left over from the freed page and hands back a slice of memory that has already been returned to the pool. A second `MessagePack::Buffer` then re-acquires that same page, so…

Timeline

Published by source

2026-07-30

Risk context

• Reported severity or threat level: low.
• Review exposure for the affected product or family: rubygems: msgpack.

Product

rubygems: msgpack

What to do

General, cautious steps (verify details in the official source):

• Review exposure and plan remediation based on risk and environment.
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-4MRV-5P47-P938

Source

GitHub

Vendor

GitHub

Published by source

2026-07-30

Last source activity

2026-07-30

Additional identifiers

CVE-2026-54522

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.