How Can I Secure My JSON Deserialization from External Sources Using Json.Net's TypeNameHandling?

External JSON Vulnerability Due to Json.Net TypeNameHandling Auto

Json.Net's TypeNameHandling auto setting can potentially introduce security risks when deserializing JSON from untrusted sources. However, these risks can be mitigated by adhering to specific guidelines.

Type Safety and Attack Gadgets

Attacks exploiting TypeNameHandling rely on constructing "attack gadgets" that execute malicious actions upon instantiation or initialization. Json.Net safeguards against these attacks by validating the compatibility of deserialized types with the expected types.

Vulnerability Conditions

While having no explicit object or dynamic members in the target class reduces the risk, it does not guarantee safety entirely. Potential vulnerabilities could arise in the following scenarios:

• Untyped Collections: Deserializing untyped collections (e.g., List