CVE-2026-48516
Received Received - Intake
Hash Collision DoS in MessagePack for C#

Publication date: 2026-06-22

Last updated on: 2026-06-22

Assigner: GitHub, Inc.

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.
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Meta Information
Published
2026-06-22
Last Modified
2026-06-22
Generated
2026-06-23
AI Q&A
2026-06-23
EPSS Evaluated
N/A
NVD
CVE-2026-48516
Affected Vendors & Products
Showing 2 associated CPEs
Vendor Product Version / Range
neuecc messagepack_for_csharp 2.5.301
neuecc messagepack_for_csharp 3.1.7
Helpful Resources
Exploitability
CWE
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KEV
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CWE ID Description
CWE-407 An algorithm in a product has an inefficient worst-case computational complexity that may be detrimental to system performance and can be triggered by an attacker, typically using crafted manipulations that ensure that the worst case is being reached.
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Executive Summary

This vulnerability exists in MessagePack for C#, specifically in versions prior to 2.5.301 and 3.1.7. The issue is that the InterfaceLookupFormatter<Tkey,TElement> constructs an internal dictionary using the default equality comparer instead of a security-aware comparer provided by the application's security options. This omission allows an attacker to exploit hash collisions, leading to a CPU denial of service attack against ILookup<TKey,TElement> even if the application has enabled untrusted-data security measures.

Impact Analysis

The vulnerability can be exploited to cause a denial of service by forcing excessive CPU usage through hash collisions. This means that an attacker can degrade or disrupt the availability of applications using the affected versions of MessagePack for C#, potentially causing performance issues or outages.

Mitigation Strategies

To mitigate this vulnerability, update MessagePack for C# to version 2.5.301 or 3.1.7 or later, where the issue has been fixed.

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