MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps

Summary ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large...

Inefficient Algorithmic Complexity

Overview MessagePack is a MessagePackMsgPack Serializer for C.NET, .NET Core, Unity, Xamarin. Affected versions of this package are vulnerable to Inefficient Algorithmic Complexity through the ExpandoObjectFormatter.Deserialize process. An attacker can cause excessive CPU consumption and memory...

EUVD-2026-38385

MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps...

GHSA-2X83-8G95-XH59 MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps

Summary ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many distinct keys can require repeated linear scans and array copies. For large...

CVE-2026-48511

Summary: CVE-2026-48511 affects MessagePack for C# where ExpandoObjectFormatter.Deserialize inserts map entries into ExpandoObject via IDictionary.Add. This insertion pattern, coupled with ExpandoObject’s internal array-like member storage, can trigger repeated linear scans and array copies, caus...

CVE-2026-48511

MessagePack for C is a MessagePack serializer for C. Prior to 2.5.301 and 3.1.7, ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many...

CVE-2026-48511 MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps

MessagePack for C is a MessagePack serializer for C. Prior to 2.5.301 and 3.1.7, ExpandoObjectFormatter.Deserialize populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. ExpandoObject internally maintains member names in array-like structures, so inserting many...

PT-2026-51395

Name of the Vulnerable Software and Affected Versions MessagePack for C versions prior to 2.5.301 MessagePack for C versions prior to 3.1.7 Description The ExpandoObjectFormatter.Deserialize function populates System.Dynamic.ExpandoObject by calling IDictionary.Add for each map entry. Because...

GHSA-92VJ-HP7M-GWCJ Nerdbank.MessagePack has Inefficient CPU Computation

Impact Applications that call OptionalConverters.WithExpandoObjectConverter and deserialize untrusted data are open to a vulnerability by which an attacker can exploit a On² algorithm to burn an inordinate amount of CPU effort by adding a great many properties to an ExpandoObject, whose Add metho...

PT-2026-47560

Impact Applications that call OptionalConverters.WithExpandoObjectConverter and deserialize untrusted data are open to a vulnerability by which an attacker can exploit a On² algorithm to burn an inordinate amount of CPU effort by adding a great many properties to an ExpandoObject, whose Add metho...