Vulnerability · Published Jun 22, 2026 · Assigned by GitHub_M
CVE-2026-48515MessagePack-CSharp: Multi-dimensional array formatters allocate from unchecked dimensions
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, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. 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-cxmj-83gh-fp49 |
| NuGet | messagepack | 3.1.7 | GHSA-cxmj-83gh-fp49 |
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