Vulnerability in MessagePack (CVE-2026-48517)
Summary
Vulnerability in MessagePack (CVE-2026-48517). Data can be tampered with by attackers. Exploitable via MessagePackSerializer.Typeless. Mitigation: upgrade to 3.1.7 or later.
Original description
The description as published by the source.
Summary
MessagePack-CSharp's typeless deserialization includes MessagePackSerializerOptions.ThrowIfDeserializingTypeIsDisallowed(Type) as a safety check for dangerous types. The default implementation checks the outer type name, but it does not recursively inspect array element types or generic type arguments.
As a result, a type that would be blocked directly can be wrapped inside an array or constructed generic type and pass the outer type check. The formatter machinery can then materialize formatters for the inner blocked type.
Impact
Applications are affected when they deserialize untrusted payloads using typeless serialization features such as MessagePackSerializer.Typeless, TypelessObjectResolver, or related typeless resolver options.
Typeless deserialization is already a high-risk feature for untrusted data, but the presence of a disallowed-type hook creates an expectation that blocked types remain blocked. This issue weakens that mitigation because the check is not applied structurally to nested type components. An attacker who can supply typeless ext-100 payloads may bypass exact outer-type blocklist checks by naming wrapper types such as arrays or generic containers.
The consequence depends on which type is reached and what the application allows typeless deserialization to instantiate. The original findings describe bypasses involving blocked or user-blocklisted gadget types.
Affected components
- Package:
MessagePack - Feature: typeless de…
Source: NIST National Vulnerability Database 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-2026-48517 has been found in MessagePack.
Attackers can target a specific entry point like MessagePackSerializer.Typeless over the network to misuse the product.
Data can be tampered with by attackers. CVSS score: 7.5/10.
What to do: upgrade MessagePack to 3.1.7 or later.
If unsure, ask your IT team or search "MessagePack CVE-2026-48517" on the vendor's site.
CVE-2026-48517 (MessagePack) — CWE-470 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: MessagePackSerializer.Typeless / TypelessObjectResolver / MessagePack / TypelessFormatter
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.
A vulnerability (CWE-470) exists in MessagePack. Attackers reach the vulnerable code path via MessagePackSerializer.Typeless without authentication.
Check the vendor advisory for the affected versions of MessagePack. Attack surface: MessagePackSerializer.Typeless / TypelessObjectResolver / MessagePack / TypelessFormatter.
Severity: High (CVSS 7.5/10). Data can be tampered with by attackers.
Update to 3.1.7.
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 'MessagePack' . 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 '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。 -
2Apply 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
References
- advisory nvd.nist.gov
- package github.com
- web github.com
- web github.com