MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6 JSON Conversion FromJsonCore recursion

Summaryinfo

A vulnerability identified as problematic has been detected in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. This vulnerability affects the function FromJsonCore of the component JSON Conversion. The manipulation leads to recursion. This vulnerability is referenced as CVE-2026-48512. Remote exploitation of the attack is possible. No exploit is available. You should upgrade the affected component.

Detailsinfo

A vulnerability was found in MessagePack-CSharp MessagePack for C# up to 2.5.300/3.1.6. It has been rated as problematic. This issue affects the function FromJsonCore of the component JSON Conversion. The manipulation with an unknown input leads to a recursion vulnerability. Using CWE to declare the problem leads to CWE-674. The product does not properly control the amount of recursion that takes place, consuming excessive resources, such as allocated memory or the program stack. Impacted is availability. The summary by CVE is:

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's JSON conversion helpers contain multiple recursion paths that do not consistently enforce a depth limit. These paths are in the JSON conversion component rather than normal typed MessagePack deserialization. MessagePackSerializer.ConvertFromJson recursively processes nested JSON arrays and objects in FromJsonCore() without consulting MessagePackSecurity.MaximumObjectGraphDepth. TinyJsonReader.ReadNextToken() recursively consumes comma and colon separator characters, allowing even malformed JSON with long separator runs to consume one stack frame per character. MessagePackSerializer.ConvertToJson applies depth checks to arrays and maps, but the typeless extension branch for ext-100 recursively calls ToJsonCore() without applying MessagePackSecurity.DepthStep(ref reader). Each path can allow attacker-controlled input to exhaust the process stack and trigger an uncatchable StackOverflowException instead of failing with a catchable parse or serialization exception. This vulnerability is fixed in 2.5.301 and 3.1.7.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-48512 since 05/21/2026. The exploitation is known to be difficult. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1499 according to MITRE ATT&CK.

Upgrading to version 2.5.301 or 3.1.7 eliminates this vulnerability.

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Productinfo

Vendor

• MessagePack-CSharp

Name

• MessagePack for C#

Version

• 2.0
• 2.1
• 2.2
• 2.3
• 2.4
• 2.5.300
• 3.1.0
• 3.1.1
• 3.1.2
• 3.1.3
• 3.1.4
• 3.1.5
• 3.1.6

CPE 2.3info

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CPE 2.2info

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