fix: Enhance security and error handling in JSON converters for Assembly, IntPtr, and UIntPtr

Author: IvanMurzak

ReflectorNet/src/Converter/Json/AssemblyJsonConverter.cs

@@ -30,20 +30,16 @@ public class AssemblyJsonConverter : JsonConverter<Assembly>
             if (string.IsNullOrWhiteSpace(assemblyName))
                 return null;
 
+            // Security: Only resolve assemblies already loaded in the AppDomain.
+            // We intentionally do NOT call Assembly.Load() to prevent loading
+            // arbitrary assemblies from untrusted JSON input.
             var assembly = AppDomain.CurrentDomain.GetAssemblies()
                 .FirstOrDefault(a => a.FullName == assemblyName || a.GetName().Name == assemblyName);
 
-            if (assembly != null)
-                return assembly;
+            if (assembly is null)
+                throw new JsonException($"Assembly '{assemblyName}' is not loaded. For security reasons, only already-loaded assemblies can be resolved.");
 
-            try
-            {
-                return Assembly.Load(assemblyName);
-            }
-            catch
-            {
-                throw new JsonException($"Unable to find or load assembly: {assemblyName}");
-            }
+            return assembly;
         }
 
         public override void Write(Utf8JsonWriter writer, Assembly? value, JsonSerializerOptions options)

ReflectorNet/src/Converter/Json/IntPtrJsonConverter.cs

@@ -32,19 +32,32 @@ public override bool CanConvert(Type typeToConvert)
                 return IntPtr.Zero;
             }
 
+            long value;
             if (reader.TokenType == JsonTokenType.Number)
             {
-                return new IntPtr(reader.GetInt64());
+                value = reader.GetInt64();
             }
-
-            if (reader.TokenType == JsonTokenType.String)
+            else if (reader.TokenType == JsonTokenType.String)
             {
                 var stringValue = reader.GetString();
-                if (long.TryParse(stringValue, out var result))
-                    return new IntPtr(result);
+                if (!long.TryParse(stringValue, out value))
+                    throw new JsonException($"Unable to parse '{stringValue}' as IntPtr.");
+            }
+            else
+            {
+                throw new JsonException($"Expected number or string token for IntPtr, but got {reader.TokenType}");
+            }
+
+            // Validate value fits in platform's IntPtr size to avoid overflow
+            if (IntPtr.Size == 4)
+            {
+                if (value < int.MinValue || value > int.MaxValue)
+                    throw new JsonException($"Value {value} is outside the range of IntPtr on this 32-bit platform.");
+
+                return new IntPtr((int)value);
             }
 
-            throw new JsonException($"Expected number or string token for IntPtr, but got {reader.TokenType}");
+            return new IntPtr(value);
         }
 
         public override void Write(Utf8JsonWriter writer, object? value, JsonSerializerOptions options)

ReflectorNet/src/Converter/Json/UIntPtrJsonConverter.cs

@@ -33,19 +33,32 @@ public override bool CanConvert(Type typeToConvert)
                 return UIntPtr.Zero;
             }
 
+            ulong value;
             if (reader.TokenType == JsonTokenType.Number)
             {
-                return new UIntPtr(reader.GetUInt64());
+                value = reader.GetUInt64();
             }
-
-            if (reader.TokenType == JsonTokenType.String)
+            else if (reader.TokenType == JsonTokenType.String)
             {
                 var stringValue = reader.GetString();
-                if (ulong.TryParse(stringValue, out var result))
-                    return new UIntPtr(result);
+                if (!ulong.TryParse(stringValue, out value))
+                    throw new JsonException($"Unable to parse '{stringValue}' as UIntPtr.");
+            }
+            else
+            {
+                throw new JsonException($"Expected number or string token for UIntPtr, but got {reader.TokenType}");
+            }
+
+            // Validate value fits in platform's UIntPtr size to avoid overflow
+            if (UIntPtr.Size == 4)
+            {
+                if (value > uint.MaxValue)
+                    throw new JsonException($"Value {value} is outside the range of UIntPtr on this 32-bit platform.");
+
+                return new UIntPtr((uint)value);
             }
 
-            throw new JsonException($"Expected number or string token for UIntPtr, but got {reader.TokenType}");
+            return new UIntPtr(value);
         }
 
         public override void Write(Utf8JsonWriter writer, object value, JsonSerializerOptions options)