CVE-2026-92707 · GHSA-qhrr-8q5h-9q3h
MessagePack: Nested arrays can blow past buffer length limits
- Risk score
- 47/100
- CVSS
- 5.3 v3.1
- Exploit chance (30 days)
- 0.6%
- Published
- 15 Oct 2026
Open in the live forecast Today's forecast
What to know
- What it is
- 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…
- Affected
- MessagePack (nuget) < 2.5.303; MessagePack (nuget) >= 3.0.0, < 3.1.9
- Fix
- Upgrade MessagePack to 2.5.303 or 3.1.9 (whichever matches your release line) or later.
- Exploitation
- No known exploitation
In the news
TL;DR
MessagePack for C# has a medium-severity vulnerability (CVSS 5.3) that can cause excessive memory allocation when deserializing attacker-controlled data. Patched versions are 2.5.303 and 3.1.9.
- The vulnerability affects MessagePack for C# prior to 2.5.303 and 3.1.9.
- SecurityWeek reports that the vulnerability is not mentioned in the press articles provided.
- No exploitation in the wild or proof-of-concept code is mentioned in the articles.
- No specific information on who is being targeted or workarounds is provided in the articles.
AI summary of 1 article.
Why it is Yellow
- CVSS 5.3 medium
- On your watchlist: NuGet
Affected packages
| Package | Ecosystem | Vulnerable | Fixed in |
|---|---|---|---|
| MessagePack | nuget | < 2.5.303 | 2.5.303 |
| MessagePack | nuget | >= 3.0.0, < 3.1.9 | 3.1.9 |
References
- https://github.com/advisories/GHSA-qhrr-8q5h-9q3h
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-qhrr-8q5h-9q3h
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/commit/7fd78bbf3476e03beae8b0f7a521125525a8a64a
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/commit/95b63fca4f7097d3cac12d1a95286af4b4bbf02c
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v2.5.303
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v3.1.9
- https://github.com/advisories/GHSA-qhrr-8q5h-9q3h
Original 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.
Last activity 15 Oct 2026. Patch Forecast updates every hour.