Vulnerability in msgpack5 (CVE-2026-107301)
Summary
Vulnerability in msgpack5 (CVE-2026-107301). Data can be tampered with by attackers. Exploitable via __proto__. Mitigation: upgrade to 6.1.0 or later.
Original description
The description as published by the source.
Impact
Passing an empty or partial options object disables the default protoAction: 'error' protection. A map containing a __proto__ key can then replace the prototype of the decoded object, potentially changing inherited properties or causing unexpected behavior in downstream code.
Only the decoded object's prototype is affected; this does not modify Object.prototype globally.
Patches
Options are now merged with secure defaults without modifying the caller's object. Unsupported protoAction values are rejected.
Workarounds
Explicitly set protoAction: 'error' whenever constructing a msgpack5 instance, and validate decoded values before use.
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-2026-107301 has been found in msgpack5.
Attackers can target a specific entry point like __proto__ over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 6.5/10.
What to do: upgrade msgpack5 to 6.1.0 or later.
If unsure, ask your IT team or search "msgpack5 CVE-2026-107301" on the vendor's site.
CVE-2026-107301 (msgpack5) — CWE-1321 / CVSS v3 6.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: __proto__ / Object.prototype / protoAction
Patched: 6.1.0 — apply immediately
Workaround: Explicitly set protoAction: 'error' whenever constructing a msgpack5 instance, and validate decoded values before use.
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.
A vulnerability (CWE-1321) exists in msgpack5. Attackers reach the vulnerable code path via __proto__ without authentication.
Check the vendor advisory for the affected versions of msgpack5. Attack surface: __proto__ / Object.prototype / protoAction.
Severity: Medium (CVSS 6.5/10). Data can be tampered with by attackers.
Update to 6.1.0.
Workaround: Explicitly set protoAction: 'error' whenever constructing a msgpack5 instance, and validate decoded values before use.
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'msgpack5' . 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
-
1Identify exposure identify
grep -r 'msgpack5' . | 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
msgpack5を grep し、稼働しているサービス・バージョンを把握する。 -
2Apply temporary workaround mitigate
Explicitly set `protoAction: 'error'` whenever constructing a msgpack5 instance, and validate decoded values before use.パッチが適用されるまでの応急処置として、Explicitly set
protoAction: 'error'whenever constructing a msgpack5 instance, and validate decoded values before use. を実施。回避策の副作用 (機能低下) を確認した上で。 -
3Apply patch patch
Upgrade msgpack5 to 6.1.0ステージング環境で 6.1.0 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。
-
4Post-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
References
- package github.com
- web github.com
- web github.com
- web github.com
- web github.com