Read the docs
TI-2026-39368 Aliases CVE-2026-54522GHSA-4mrv-5p47-p938

MessagePack::Buffer#clear Use-After-Free that Enables Cross-Buffer Disclosure

Priority MEDIUM 44CWE-416Published · Updated

Key facts

Attack vector
Local
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
Present
Impact type
—
Confidentiality · integrity · availability
Low · None · None
Fix status
Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and GitHub.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00227 13th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed msgpack-ruby (msgpack): 1.8.2msgpack (RubyGems): 1.8.2

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
msgpackmsgpack-rubybefore 1.8.21.8.2Patch availableCNA
—msgpack (RubyGems)before 1.8.21.8.2Patch availableGHSA-4mrv-5p47-p938
  • msgpack-ruby Vendormsgpack Affected before 1.8.2 Fixed in 1.8.2 Patch available CNA
  • msgpack (RubyGems) Vendor— Affected before 1.8.2 Fixed in 1.8.2 Patch available GHSA-4mrv-5p47-p938

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:msgpack:messagepack:*:*:*:*:*:ruby:*:*before 1.8.2Vulnerablemsgpack
  • cpe:2.3:a:msgpack:messagepack:*:*:*:*:*:ruby:*:* Versions before 1.8.2 Vulnerable ·msgpack

Remediation

  • Fix · CNA msgpack-ruby (msgpack) Fixed in 1.8.2
  • Fix · GHSA-4mrv-5p47-p938 msgpack (RubyGems) Fixed in 1.8.2 Advisory →

Vendor assessments

Red Hat

Red Hat's page for this CVE →

Not affected: 1 product
  • Red Hat

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-54522
  2. 2026-10-03 Alias added: GHSA-4mrv-5p47-p938
  3. 2026-11-06 Affected versions changed · Red Hat
  4. 2026-11-06 CVSS score added · Red Hat

References

Exploit 1

Patch 1

Other 3

  • TI-2026-17336 Uncontrolled resource consumption in msgpack-java CVSS 3.1HIGH 7.5
  • TI-2026-41435 MessagePack: Out-of-bounds read/crash on Unpacker reuse after caught error CVSS 3.1HIGH 7.5

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences