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CVE-2026-48509
critical
CVSS 9.1
Vulnerability in MessagePack (CVE-2026-48509)
Summary
vulnerability in MessagePack (CVE-2026-48509). Data can be tampered with by attackers. Exploitable via ``MessagePackSerializerOptions.Standard``. Mitigation: upgrade to `3.1.7` or later.
AI summary snake-internal / snake-material-v2
A vulnerability tracked as **CVE-2026-48509** has been found in MessagePack.
Attackers can target a specific entry point like ``MessagePackSerializerOptions.Standard`` over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 9.1/10.
What to do: upgrade MessagePack to **3.1.7** or later.
If unsure, ask your IT team or search "MessagePack CVE-2026-48509" on the vendor's site.
CVE-2026-48509 (MessagePack) — CWE-1188 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: `MessagePackSerializerOptions.Standard` / `MessagePackSecurity.TrustedData` / `MessagePackSecurity.UntrustedData` / `MessagePack.AspNetCoreMvcFormatter`
Patched: `3.1.7` — 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.
❓ What is the problem
**A vulnerability** (CWE-1188) exists in MessagePack. Attackers reach the vulnerable code path via ``MessagePackSerializerOptions.Standard`` without authentication.
📍 Affected scope
MessagePack — . Attack surface: `MessagePackSerializerOptions.Standard` / `MessagePackSecurity.TrustedData` / `MessagePackSecurity.UntrustedData` / `MessagePack.AspNetCoreMvcFormatter`.
🔥 Severity
Severity: Critical (CVSS 9.1/10). Data can be tampered with by attackers
🔧 How to fix
Update to **3.1.7**.
🛡️ Workaround
Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.
🔍 Detection
Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run `grep -r 'MessagePack' .` against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.
Response Actions (7 steps)
Concrete steps and command examples for SOC/SRE teams to execute in order
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1Identify exposure identify
grep -r 'MessagePack' . | 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 `MessagePack` を grep し、稼働しているサービス・バージョンを把握する。
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6Apply patch patch
Upgrade MessagePack to 3.1.7ステージング環境で 3.1.7 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と、Step 3 で見つけた異常検知の続報チェックを含めること。
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7Post-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 Step 3 と同じログクエリでアラート再発が無いか継続監視。
Affected packages
nuget
MessagePack
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"3.1.7"}]}]