Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-48514MessagePack-CSharp: Unity unsafe blit formatter allocates from unbounded byte length
Medium 6.3
In plain English
A medium-severity resource allocation without limits in MessagePack-CSharp from MessagePack-CSharp. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 35% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| NuGet | messagepack | 2.5.301 | GHSA-w567-gjr2-hm5j |
| NuGet | messagepack | 3.1.7 | GHSA-w567-gjr2-hm5j |
Affected products (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MessagePack-CSharp | MessagePack-CSharp | >= 3.0, < 3.1.7< 2.5.301 |
Weakness: CWE-770 · Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N