CVE-2018-0765 in .NET Framework
Summary
by MITRE
A denial of service vulnerability exists when .NET and .NET Core improperly process XML documents, aka ".NET and .NET Core Denial of Service Vulnerability." This affects Microsoft .NET Framework 2.0, Microsoft .NET Framework 3.0, Microsoft .NET Framework 4.7.1, Microsoft .NET Framework 4.6/4.6.1/4.6.2/4.7/4.7.1, Microsoft .NET Framework 4.5.2, Microsoft .NET Framework 4.7/4.7.1, Microsoft .NET Framework 4.6, Microsoft .NET Framework 3.5, Microsoft .NET Framework 3.5.1, Microsoft .NET Framework 4.6/4.6.1/4.6.2, Microsoft .NET Framework 4.6.2/4.7/4.7.1, .NET Core 2.0, Microsoft .NET Framework 4.7.2.
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Analysis
by VulDB Data Team • 03/11/2023
The vulnerability identified as CVE-2018-0765 represents a critical denial of service weakness in Microsoft's .NET Framework and .NET Core implementations that stems from improper handling of XML documents. This flaw exists within the core XML processing libraries that form the foundation of numerous applications built on these platforms, making it a widespread concern across the enterprise software ecosystem. The vulnerability specifically manifests when applications process malformed or specially crafted XML input through the .NET XML parsers, leading to system instability and potential service disruption. Security researchers have classified this issue under CWE-400, which denotes "Uncontrolled Resource Consumption" or "Resource Exhaustion," indicating that the flaw allows malicious actors to consume excessive system resources through carefully constructed XML payloads. The impact extends across multiple versions of the .NET Framework and .NET Core, including versions 2.0, 3.0, 4.5.2, 4.6, 4.6.1, 4.6.2, 4.7, 4.7.1, 4.7.2, and the corresponding .NET Core 2.0 implementation, demonstrating the broad scope of affected systems.
The technical exploitation of this vulnerability occurs through XML External Entity (XXE) processing flaws or malformed XML structures that cause the .NET XML parsers to enter infinite loops or consume excessive memory resources. When applications process XML documents containing recursive references, large nested structures, or specially crafted entities, the underlying XML processing libraries fail to properly validate or limit resource consumption, leading to system resource exhaustion. This behavior aligns with ATT&CK technique T1499.004, which describes "File System Wipe" through resource exhaustion attacks, although the specific implementation here targets memory and CPU consumption rather than direct file system destruction. The vulnerability can be triggered through various XML processing methods including XmlReader, XmlDocument, and XDocument classes, making it particularly dangerous as it can be exploited through common XML parsing operations that are fundamental to many applications. Attackers can construct malicious XML documents that cause the .NET runtime to continuously process elements without proper termination, resulting in denial of service conditions that can crash applications or make systems unresponsive.
The operational impact of CVE-2018-0765 extends beyond simple service disruption, as it can affect critical business applications that rely heavily on XML processing for data exchange, configuration management, or web service communications. Organizations running applications that process external XML input, such as web services, enterprise integration platforms, or content management systems, face significant risk from this vulnerability. The exploitation can lead to complete application crashes, requiring system restarts and potentially causing extended downtime that impacts business operations. This vulnerability is particularly concerning in cloud environments or containerized applications where resource limits may be more constrained, as the resource exhaustion can affect not just individual applications but entire hosting environments. The attack surface is broad since XML processing is used extensively across different application types, from simple web forms to complex enterprise integration solutions, making it difficult for organizations to identify all potentially vulnerable systems. Security teams must consider this vulnerability in their risk assessments and incident response planning, as it can be leveraged as part of broader attack campaigns targeting system availability.
Organizations should implement immediate mitigations including applying the relevant Microsoft security updates and patches released in response to this vulnerability. The recommended approach involves updating to the latest .NET Framework and .NET Core versions that contain the necessary fixes, as Microsoft has provided specific patches for affected versions. Additionally, implementing input validation measures and XML schema validation can help prevent exploitation by filtering out malformed XML content before it reaches the vulnerable parsing libraries. Network segmentation and application whitelisting can limit the potential attack surface, while monitoring for unusual resource consumption patterns can help detect exploitation attempts. Organizations should also consider implementing XML processing restrictions within their applications, such as limiting the maximum depth of XML structures or setting resource limits for XML parsing operations. The vulnerability's classification under CWE-400 emphasizes the importance of implementing proper resource management and validation controls, while the ATT&CK framework guidance suggests incorporating defensive measures that monitor for resource exhaustion patterns and limit the impact of such attacks. Regular security assessments and penetration testing should include verification of XML processing components to ensure that the implemented mitigations are effective against this specific vulnerability.