EUVD-2026-330303

fkie_cve-2026-48514

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, UnsafeBlitFormatterBase<T>.Deserialize reads an attacker-controlled byteLength from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes. The outer extension header is bounded by available input, but that bound is not used to constrain the inner byteLength before allocation. A very small payload can therefore request a very large T[] allocation. This vulnerability is fixed in 2.5.301 and 3.1.7.

GHSA-w567-gjr2-hm5j — MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length

Affected: NuGet: MessagePack

## Summary

`UnsafeBlitFormatterBase<T>.Deserialize` reads an attacker-controlled `byteLength` from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes.

The outer extension header is bounded by available input, but that bound is not used to constrain the inner `byteLength` before allocation. A very small payload can therefore request a very large `T[]` allocation.

## Impact

Applications are affected when they deserialize untrusted payloads using Unity blit resolvers such as `UnityBlitResolver` or `UnityBlitWithPrimitiveArrayResolver`.

This is especially relevant to Unity multiplayer clients or servers that use MessagePack-CSharp for networked values such as vectors, matrices, or primitive arrays. A hostile peer can send an extension payload with a large declared byte length and cause an out-of-memory exception or process termination on memory-constrained platforms.

The resolver is opt-in, but the vulnerable value is pure wire input and the allocation happens before the formatter verifies that the declared bytes are actually present in the extension body.

## Affected components

- Package: `MessagePack.UnityClient` - Resolvers: `UnityBlitResolver`, `UnityBlitWithPrimitiveArrayResolver` - API: `UnsafeBlitFormatterBase<T>.Deserialize` - Finding IDs: `MESSAGEPACKCSHARP-080`, duplicate/open variant `MESSAGEPACKCSHARP-OPEN-010`

## Patches

Fixes are prepared and will be released…

Most recent entries from all

EUVD-2026-330303

fkie_cve-2026-48514

GHSA-w567-gjr2-hm5j — MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length