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Vulnerability record · CVE-2026-48516 · published 22 June 2026

CVE-2026-48516: Messagepack vulnerability

Messagepack · Messagepack

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.

6.3 CVSS 4.0 Medium EPSS 0.40% · top 67.9% CWE-407 · CWE-407
6.3CVSS 4.0 base score
0.40%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
25 Jun 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-q2h6-ghwm-5qm8 MitigationVendor Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

8.2CVE-2026-48502Messagepack out-of-bounds read vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePackReader.ReadDateTime() can allocate stack memory based o…EPSS 0.44%8.2CVE-2026-48109Messagepack improper input validation vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, A vulnerability exists in the optional LZ4 decompression path used…EPSS 0.51%7.5CVE-2026-48506Messagepack vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePackReader.TrySkip() recursively descends into nested array…EPSS 0.47%6.5CVE-2020-5234Messagepack stack-based buffer overflow vulnerabilityMessagePack for C# and Unity before version 1.9.11 and 2.1.90 has a vulnerability where untrusted data can lead to DoS attack due to hash collisions …EPSS 1.6%6.3CVE-2026-48513Messagepack vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, runtime-generated union deserializers emitted by DynamicUnionResol…EPSS 0.40%6.3CVE-2026-48514Messagepack allocation without limits vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, UnsafeBlitFormatterBase<T>.Deserialize reads an attacker-controlle…EPSS 0.40%6.3CVE-2026-48515Messagepack allocation without limits vulnerabilityMessagePack 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 dimen…EPSS 0.40%6.3CVE-2026-48517Messagepack deserialization of untrusted data vulnerabilityMessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's typeless deserialization includes MessagePack…EPSS 0.35%

Source: NIST National Vulnerability Database (record CVE-2026-48516), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.