What’s Vulnerable › Vulnerabilities
CVE-2026-48516: MessagePack-CSharp: InterfaceLookupFormatter bypasses collision-resistant comparer settings
- Severity: high (CVSS 7.5 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.4% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-06-22 · updated 2026-06-25
- Weakness: CWE-407
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.
Affected products
- MessagePack-CSharp: before 2.5.301; from 3.0.3 before 3.1.7 — fixed in 2.5.301, 3.1.7
How to fix
Upgrade to a fixed version: MessagePack-CSharp 2.5.301, 3.1.7. Check the vendor advisory for mitigations.
References
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