CVE-2026-48516
High
Description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, InterfaceLookupFormatter<TKey,TElement> constructs an internal Dictionary<TKey, IGrouping<TKey,TElement>> with the default equality comparer instead of the security-aware comparer supplied by options.Security.GetEqualityComparer<TKey>(). This formatter omission allows hash-collision CPU denial of service against ILookup<TKey,TElement> even when the application has opted into the untrusted-data security posture This vulnerability is fixed in 2.5.301 and 3.1.7.
SeverityHigh
CVSS7.5
Exploit probability—
ProductMessagepack
PublishedJun 22, 2026
First seenJun 22, 2026
Weakness typeCWE-407CWE-407
How to fix
Update
- messagepack messagepack2.5.301, 3.1.7 or later
- MessagePack2.5.301, 3.1.7 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| messagepack messagepack | v < 2.5.301, 3.0.3 ≤ v < 3.1.7 | 2.5.301, 3.1.7 |
| MessagePackNuGet | v < 2.5.301, 3.0 ≤ v < 3.1.7 | 2.5.301, 3.1.7 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
In the Intelligence 360 plan
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.