Vulnerability in MessagePack (CVE-2026-48516)
Summary
Vulnerability in MessagePack (CVE-2026-48516). Risk of unauthorized operations or information disclosure. Exploitable via MessagePackSecurity.UntrustedData. Mitigation: upgrade to 3.1.7 or later.
Original description
The description as published by the source.
Summary
InterfaceLookupFormatter constructs an internal Dictionary> with the default equality comparer instead of the security-aware comparer supplied by options.Security.GetEqualityComparer().
Other hash-based collection formatters use the security-aware comparer when MessagePackSecurity.UntrustedData is configured. This formatter omission allows hash-collision CPU denial of service against ILookup even when the application has opted into the untrusted-data security posture.
Impact
Applications are affected when they deserialize untrusted payloads into schemas containing ILookup with a key type for which attacker-controlled hash collisions are feasible.
Under the default comparer, many colliding keys can degrade dictionary insertion from amortized constant time to quadratic behavior. A payload of colliding keys can consume CPU for a disproportionate amount of time. This bypasses the mitigation that developers intentionally enabled by using MessagePackSecurity.UntrustedData.
Affected components
- Package:
MessagePack - API:
InterfaceLookupFormatter.Create - Data type:
ILookup - Finding ID:
MESSAGEPACKCSHARP-041
Patches
Fixes are prepared and will be released in coordinated patch versions.
Upgrade guidance:
- Upgrade
MessagePackto the patched version for your release line. - Upgrade companion MessagePack packages in the same dependency graph to the coordinated patched versions.
The fix should create the internal dictionary wit…
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-2026-48516 has been found in MessagePack.
Attackers can target a specific entry point like MessagePackSecurity.UntrustedData over the network to misuse the product.
Risk of unauthorized operations or information disclosure. 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-2026-48516" on the vendor's site.
CVE-2026-48516 (MessagePack) — CWE-407 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: MessagePackSecurity.UntrustedData / MessagePack / InterfaceLookupFormatter
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-407) exists in MessagePack. Attackers reach the vulnerable code path via MessagePackSecurity.UntrustedData without authentication.
Check the vendor advisory for the affected versions of MessagePack. Attack surface: MessagePackSecurity.UntrustedData / MessagePack / InterfaceLookupFormatter.
Severity: High (CVSS 7.5/10). Risk of unauthorized operations or information disclosure.
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