CVE-2026-92707
MessagePack: Nested arrays can blow past buffer length limits
Published Oct 15, 2026 · updated Oct 15, 2026
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an 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 , or otherwise use a resolver path that selects ; 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 and has a reachable hub method with an parameter may pass attacker-controlled arguments to the vulnerable MessagePack-CSharp formatter. However, the underlying vulnerability is in MessagePack-CSharp, not SignalR, and other applications that deserialize untrusted data through the same formatter may also be affected. MessagePack-CSharp 2.5.302 is confirmed to contain the vulnerable code. Other releases containing the same allocate-before-depth-check behavior may also be affected. Authentication requirements depend on the application exposing the deserialization endpoint: exploitation require
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Oct 15, 2026 · GitHub Advisory Database
Detected
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an 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 simultan
Oct 15, 2026 · GitHub Advisory Database
Updated
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an 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 simultan
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 2.5.303; MessagePack fixed in 3.1.9
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 2.5.303
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 3.1.9
Oct 15, 2026 · NIST NVD
Updated
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 sa
Affected
- NuGet MessagePack0 → 2.5.303
- NuGet MessagePack3.0.0 → 3.1.9
- nuget MessagePack< 2.5.303
- nuget MessagePack>= 3.0.0, < 3.1.9
- nuget messagepackversion unspecified
Sources
- CVE.orgVulnerability recordCVE-2026-92707
Official CVE identifier
cve.org - GitHub Advisory DatabasePackage advisoryGHSA-qhrr-8q5h-9q3h
GitHub Advisory Database record mirrored by OSV.
github.com - GitLab Advisory DatabasePackage advisoryCVE-2026-92707
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
advisories.gitlab.com - NIST NVDVulnerability recordCVE-2026-92707
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 ar
nvd.nist.gov - OSV.devPackage advisoryGHSA-qhrr-8q5h-9q3h
MessagePack: Nested arrays can blow past buffer length limits
osv.dev