MessagePack: Nested arrays can blow past buffer length limits

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-92707
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-15 19:17:48 UTC
Updated2026-10-16 16:00:33 UTC
DescriptionMessagePack 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.

Risk And Classification

Primary CVSS: v3.1 5.3 MEDIUM from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Problem Types: CWE-1325 | CWE-1325 CWE-1325: Improperly Controlled Sequential Memory Allocation

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
3.1CNADECLARED5.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA MessagePack-CSharp MessagePack-CSharp affected < 2.5.303 Not specified
CNA MessagePack-CSharp MessagePack-CSharp affected >= 3.0.0, < 3.1.9 Not specified

References

ReferenceSourceLinkTags
github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHS... [email protected] github.com
github.com/MessagePack-CSharp/MessagePack-CSharp/commit/95b63fca4f7097d3... [email protected] github.com
github.com/MessagePack-CSharp/MessagePack-CSharp/commit/7fd78bbf3476e03b... [email protected] github.com
github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v2.5.303 [email protected] github.com
github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v3.1.9 [email protected] github.com
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