Use-After-Free in msgpack (CVE-2026-54522)
Summary
Vulnerability in msgpack (CVE-2026-54522). Risk of unauthorized operations or information disclosure. Exploitable via rmem_last. Mitigation: upgrade to 1.8.2 or later.
Original description
The description as published by the source.
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.
Source: GitHub Security Advisories (Global) NVD GitHub Advisory
Auto-generated summary
Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.
A vulnerability tracked as CVE-2026-54522 has been found in msgpack.
Attackers can target a specific entry point like rmem_last over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.4/10.
What to do: upgrade msgpack to 1.8.2 or later.
If unsure, ask your IT team or search "msgpack CVE-2026-54522" on the vendor's site.
CVE-2026-54522 (msgpack) — CWE-416 / CVSS v3 5.4
Attack vector: remote (network-reachable) / no user interaction
Attack surface: rmem_last / rmem_end / rmem_owner / _msgpack_buffer_chunk_destroy
Patched: 1.8.2 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.
Use-after-free (CWE-416) exists in msgpack. Attackers reach the vulnerable code path via rmem_last.
Check the vendor advisory for the affected versions of msgpack. Attack surface: rmem_last / rmem_end / rmem_owner / _msgpack_buffer_chunk_destroy.
Severity: Medium (CVSS 5.4/10). Risk of unauthorized operations or information disclosure.
Update to 1.8.2.
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'msgpack' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response actions
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'msgpack' . | grep -v node_modulesリポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で
msgpackを grep し、稼働しているサービス・バージョンを把握する。 -
2Apply patch patch
Upgrade msgpack to 1.8.2ステージング環境で 1.8.2 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
-
3Post-deployment verification verify
Confirm patched version is live in productionパッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。
Affected packages
Fix status by distribution
Fixed packages published by each distribution for this CVE
- Debian DEBIAN-CVE-2026-54522 ruby-msgpack
- Ubuntu UBUNTU-CVE-2026-54522 ruby-msgpack
References
- advisory github.com
- advisory github.com
- advisory nvd.nist.gov
- patch github.com
- web github.com
- web cve.org
- web github.com