Description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared array length before the configured object-graph depth limit rejects the input, while nested array headers can reuse the same trailing unread bytes to satisfy per-header length validation. A comparatively small payload can therefore keep many large arrays alive at once. When an attacker can submit such data repeatedly, the allocations can cause severe managed-heap pressure, excessive garbage collection, process termination, or loss of service. Exposure requires an application to deserialize untrusted data through the affected formatter path and permit repeated attacker-controlled submissions, such as a reachable ASP.NET Core SignalR hub method with an object parameter and AddMessagePackProtocol() enabled. This issue is fixed in versions 2.5.303 and 3.1.9.
Published: 2026-10-15
Score: 5.3 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

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Remediation

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Tracking

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Advisories
Source ID Title
Github GHSA Github GHSA GHSA-qhrr-8q5h-9q3h MessagePack: Nested arrays can blow past buffer length limits
History

Thu, 15 Oct 2026 21:30:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Thu, 15 Oct 2026 18:45:00 +0000

Type Values Removed Values Added
Description MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared array length before the configured object-graph depth limit rejects the input, while nested array headers can reuse the same trailing unread bytes to satisfy per-header length validation. A comparatively small payload can therefore keep many large arrays alive at once. When an attacker can submit such data repeatedly, the allocations can cause severe managed-heap pressure, excessive garbage collection, process termination, or loss of service. Exposure requires an application to deserialize untrusted data through the affected formatter path and permit repeated attacker-controlled submissions, such as a reachable ASP.NET Core SignalR hub method with an object parameter and AddMessagePackProtocol() enabled. This issue is fixed in versions 2.5.303 and 3.1.9.
Title MessagePack: Nested arrays can blow past buffer length limits
Weaknesses CWE-1325
References
Metrics cvssV3_1

{'score': 5.3, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L'}

Subscriptions

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cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2026-10-15T20:12:15.468Z

Reserved: 2026-09-16T16:22:31.542Z

Link: CVE-2026-92707

cve-icon Vulnrichment

Updated: 2026-10-15T20:12:09.856Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-15T19:17:48.703

Modified: 2026-10-16T16:00:33.533

Link: CVE-2026-92707

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.

Weaknesses
  • CWE-1325

    Improperly Controlled Sequential Memory Allocation