MessagePack: Nested arrays can blow past buffer length limits

• < 2.5.303

### 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

GitHub Advisory Database

• >= 3.0.0, < 3.1.9

### 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

GitHub Advisory Database