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Newtonsoft JSON's TypeNameHandling.All
: Security Implications
Newtonsoft JSON's documentation strongly cautions against using TypeNameHandling.All
for deserializing JSON from untrusted sources. This article explores the potential security vulnerabilities associated with this setting and outlines mitigation strategies.
Vulnerabilities of TypeNameHandling.All
The TypeNameHandling.All
setting allows Newtonsoft JSON to instantiate types based on metadata within the JSON payload. While convenient, this creates a significant security risk. An attacker can craft malicious JSON that forces the deserialization of harmful types, leading to arbitrary code execution.
For instance, a benign JSON payload might look like this:
<code class="language-json">{ "$type": "Car", "Maker": "Ford", "Model": "Explorer" }</code>
However, a malicious actor could construct a payload targeting a system-level type:
<code class="language-json">{ "$type": "System.CodeDom.Compiler.TempFileCollection", "BasePath": "%SYSTEMDRIVE%", "KeepFiles": "false", "TempDir": "%SYSTEMROOT%" }</code>
This would cause Newtonsoft JSON to create a TempFileCollection
instance, potentially deleting arbitrary files on the system by manipulating BasePath
and TempDir
.
Effective Mitigation: Custom SerializationBinder
The key to securing JSON deserialization with type information is using a custom SerializationBinder
. This allows for strict control over which types are permitted during deserialization, effectively preventing the instantiation of malicious types.
Implementing a custom SerializationBinder
involves these steps:
IBindingSerializer
interface.BindToName
method to enforce type validation. This typically involves checking the type against a whitelist or blacklist.SerializationBinder
with the Newtonsoft JSON serializer.By implementing these steps, you can safely deserialize JSON from external sources while preventing potentially harmful type instantiations. This proactive approach significantly reduces the risk of exploitation.
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