CVE-2026-83520 in .NET
Summary
by MITRE • 10/13/2026
Deserialization of untrusted data in .NET allows an unauthorized attacker to execute code over a network.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability described involves the deserialization of untrusted data within the Microsoft .NET framework, which represents a critical security flaw allowing for remote code execution. Deserialization is the process by which serialized objects are converted back into their original state in memory. When an application accepts serialized data from an external or untrusted source without proper validation or sanitization, it creates a significant attack vector. Attackers can craft malicious payloads that exploit specific types during the deserialization process, leading to arbitrary code execution on the target system with the privileges of the running application. This type of vulnerability is particularly dangerous because it bypasses traditional network security controls and allows direct interaction with the underlying operating system through the compromised application logic.
From a technical perspective, this flaw aligns closely with CWE-502, which denotes Deserialization of Untrusted Data. The root cause typically lies in the use of insecure deserializers such as BinaryFormatter, SoapFormatter, or XmlSerializer when processing data that originates from users or external services. These serializers often allow for polymorphic calls and can instantiate arbitrary types if not strictly constrained. An attacker constructs a specially crafted serialized object containing malicious logic within its constructor or property setters. When the vulnerable application processes this input, it inadvertently executes the embedded code during the reconstruction of the object graph. This mechanism enables attackers to achieve full system compromise, including data theft, lateral movement, and persistence establishment, depending on the context in which the .NET application is running.
The operational impact of this vulnerability is severe, as it effectively grants an unauthorized attacker complete control over the affected server or service. Since many enterprise applications rely heavily on serialization for inter-process communication, API interactions, and state management, a successful exploit can lead to widespread disruption. Beyond immediate code execution, attackers may leverage this access to exfiltrate sensitive data, modify system configurations, install backdoors, or pivot into other parts of the network infrastructure. The ability to execute arbitrary commands means that standard security boundaries are rendered ineffective, as the attacker operates within the trusted context of the application process itself.
Mitigation strategies must focus on eliminating the use of insecure deserializers and implementing strict input validation. Organizations should replace legacy serializers like BinaryFormatter with safer alternatives such as JSON.NET or System.Text.Json, which do not support arbitrary type instantiation by default. If serialization is necessary, developers should implement allow-lists to restrict the types that can be instantiated during deserialization. Additionally, integrating security testing tools into the development lifecycle helps identify vulnerable code patterns early. Network-level controls like web application firewalls may offer some protection but are insufficient as a primary defense due to the complexity of detecting obfuscated malicious payloads in serialized data streams. Regular patching and adherence to secure coding guidelines outlined by industry standards such as OWASP Top 10, specifically under Injection categories related to object injection, remain essential for preventing exploitation.