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CVE-2026-92707 medium CVSS 5.3

Vulnerability in MessagePack (CVE-2026-92707)

Summary

Vulnerability in MessagePack (CVE-2026-92707). Risk of unauthorized operations or information disclosure. Exploitable via System.Object. Mitigation: upgrade to 3.1.9 or later.

Original description

The description as published by the source.

Impact

MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into System.Object.

When PrimitiveObjectFormatter encounters an array, it allocates an object[] using the declared array length before enforcing the configured maximum object-graph depth. A specially crafted payload containing deeply nested arrays can therefore keep many large arrays live simultaneously before deserialization is rejected for exceeding the depth limit.

Because the array-header validation uses the total unread byte count as evidence that the declared elements may be present, nested array headers can reuse the same trailing bytes for this validation. This permits a relatively small payload to cause disproportionately large managed-heap allocations. The reported example uses an approximately 31.5 KiB payload to allocate roughly 114.7 MiB of reference storage on x64—an amplification factor of approximately 3,800—before the depth exception is raised. Repeated requests may cause severe memory pressure, excessive garbage collection, process termination, or loss of service availability.

Applications are affected when they:

  • Deserialize untrusted MessagePack data as object, or otherwise use a resolver path that selects PrimitiveObjectFormatter; and
  • Permit an attacker to submit such data repeatedly.

ASP.NET Core SignalR is one known way to expose the vulnerability remotely: an application that enables `Ad…

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-2026-92707 has been found in MessagePack.
Attackers can target a specific entry point like System.Object over the network to misuse the product.
Risk of unauthorized operations or information disclosure. CVSS score: 5.3/10.
What to do: upgrade MessagePack to 3.1.9 or later.
If unsure, ask your IT team or search "MessagePack CVE-2026-92707" on the vendor's site.

CVE-2026-92707 (MessagePack) — CWE-1325 / CVSS v3 5.3
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: System.Object / PrimitiveObjectFormatter / object
Patched: 3.1.9 — 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-1325) exists in MessagePack. Attackers reach the vulnerable code path via System.Object without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of MessagePack. Attack surface: System.Object / PrimitiveObjectFormatter / object.

🔥 Severity

Severity: Medium (CVSS 5.3/10). Risk of unauthorized operations or information disclosure.

🔧 How to fix

Update to 3.1.9.

🛡️ 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

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify 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。

  2. 2
    Apply patch patch 
    Upgrade MessagePack to 3.1.9

    ステージング環境で 3.1.9 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。

  3. 3
    Post-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

nuget MessagePack
[{"type":"ECOSYSTEM","events":[{"introduced":"3.0.0"},{"fixed":"3.1.9"}]}]

References

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