CVE-2016-0033 in Windows
Summary
by MITRE
Microsoft .NET Framework 2.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, and 4.6.1 does not prevent recursive compilation of XSLT transforms, which allows remote attackers to cause a denial of service (performance degradation) via crafted XSLT data, aka ".NET Framework Stack Overflow Denial of Service Vulnerability."
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Analysis
by VulDB Data Team • 07/07/2022
The vulnerability identified as CVE-2016-0033 represents a critical denial of service weakness within Microsoft .NET Framework versions 2.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, and 4.6.1. This flaw specifically targets the XSLT (Extensible Stylesheet Language Transformations) processing capabilities of the framework, creating a condition where recursive compilation of XSLT transforms can occur without proper safeguards. The vulnerability stems from insufficient validation mechanisms that should prevent infinite recursion during XSLT transformation operations, allowing malicious actors to craft specially designed XSLT data that triggers excessive resource consumption.
The technical implementation of this vulnerability exploits the inherent recursive nature of XSLT processing within the .NET Framework. When an application processes XSLT transformations, the framework typically maintains a call stack to track transformation operations. In the presence of this vulnerability, malicious XSLT code can create circular references or nested transformations that cause the framework to continuously compile and recompile the same transformation elements. This recursive behavior leads to rapid stack exhaustion and performance degradation that can ultimately result in system unresponsiveness or complete denial of service. The flaw operates at the core processing level of the .NET Framework's XSLT engine, making it particularly dangerous as it affects applications across multiple framework versions and deployment scenarios.
From an operational impact perspective, this vulnerability presents significant risks to organizations relying on .NET Framework applications that process external XSLT data. Attackers can exploit this weakness by submitting crafted XSLT files or data streams that contain recursive transformation references, causing target systems to consume excessive CPU cycles and memory resources. The performance degradation can manifest as slow response times, application hangs, or complete system crashes, particularly affecting web applications, enterprise systems, and services that process user-generated content or external data feeds. This vulnerability directly aligns with the ATT&CK technique T1499.004 for Network Denial of Service and represents a classic stack overflow scenario that can be amplified through recursive processing patterns. The vulnerability is particularly concerning in environments where .NET applications handle untrusted input data, as it can be exploited without requiring authentication or elevated privileges.
Organizations should implement immediate mitigations including input validation and sanitization of all XSLT data sources to prevent recursive transformation patterns, application-level rate limiting to restrict processing of large or complex XSLT files, and deployment of updated .NET Framework versions that address this specific recursion issue. Microsoft released patches for this vulnerability through security updates, and administrators should ensure all affected systems receive these updates promptly. Additionally, implementing proper monitoring and alerting mechanisms can help detect unusual resource consumption patterns that may indicate exploitation attempts. The vulnerability demonstrates the importance of proper input validation and recursion detection in processing engines, aligning with CWE-674 principle of preventing uncontrolled recursion in software systems. Organizations should also consider implementing network segmentation and application firewalls to limit exposure of .NET applications that process external XSLT content, reducing the attack surface for this specific vulnerability.