CVE-2016-3255 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 allows remote attackers to read arbitrary files via XML data containing an external entity declaration in conjunction with an entity reference, related to an XML External Entity (XXE) issue, aka ".NET Information Disclosure Vulnerability."
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Analysis
by VulDB Data Team • 09/01/2022
The vulnerability identified as CVE-2016-3255 represents a critical XML External Entity (XXE) flaw within Microsoft .NET Framework versions 2.0 SP2, 3.5, 3.5.1, 4.5.2, 4.6, and 4.6.1. This issue stems from the framework's insufficient validation of XML data processing, specifically when handling external entity declarations and references. The vulnerability falls under CWE-611, which categorizes improper restriction of XML external entities, and aligns with ATT&CK technique T1213.002 for data from information repositories. Attackers can exploit this weakness by crafting malicious XML payloads that include external entity declarations pointing to local files on the target system, followed by entity references that trigger file reading operations. The flaw enables unauthorized information disclosure, allowing remote adversaries to access sensitive files that should remain protected within the application's file system. This vulnerability is particularly dangerous because it can be leveraged to extract configuration files, database credentials, application source code, and other confidential data from systems running affected .NET Framework versions.
The technical exploitation of CVE-2016-3255 occurs when applications processing XML data fail to properly sanitize external entity references, creating a pathway for attackers to bypass normal access controls. The vulnerability manifests when an application uses XML parsers that do not disable external entity resolution, particularly in scenarios where XML data is processed from untrusted sources. This flaw operates at the application layer and can be triggered through various attack vectors including web services, file upload functionalities, and API endpoints that accept XML input. The XXE attack pattern enables attackers to perform server-side request forgery attacks, potentially leading to directory traversal, local file inclusion, and information disclosure. When combined with other techniques such as path traversal or local file inclusion, this vulnerability can provide attackers with comprehensive access to the underlying file system. The impact extends beyond simple information disclosure, as attackers can potentially extract system configuration files, application secrets, and other sensitive data that may reveal additional attack vectors or system weaknesses.
The operational impact of CVE-2016-3255 is severe for organizations running affected .NET Framework versions, as it provides a straightforward method for remote attackers to extract sensitive information from systems without requiring authentication or elevated privileges. This vulnerability can affect web applications, enterprise services, and any system that processes XML data from external sources, potentially compromising entire application environments. Organizations may experience data breaches, regulatory compliance violations, and reputational damage when this vulnerability is exploited successfully. The attack surface is particularly broad given that many enterprise applications rely on .NET Framework for their web services and backend processing capabilities. Additionally, the vulnerability can be chained with other exploits to create more sophisticated attack scenarios, including privilege escalation or lateral movement within network environments. The vulnerability's presence in multiple .NET Framework versions means that organizations must assess and patch all affected systems across their infrastructure, potentially requiring extensive testing to ensure compatibility and prevent service disruptions.
Mitigation strategies for CVE-2016-3255 should focus on disabling external entity resolution in XML parsers and implementing comprehensive input validation controls. Organizations must ensure that XML parsers are configured to reject external entity declarations and references, particularly in applications processing untrusted XML data. The recommended approach includes updating to patched versions of Microsoft .NET Framework, which contain fixes for the XXE vulnerability. Security controls should also implement proper XML schema validation, input sanitization, and content filtering to prevent malicious XML content from being processed. Network segmentation and access controls can help limit the potential impact of successful exploitation by restricting access to sensitive systems and data repositories. Additionally, organizations should conduct comprehensive vulnerability assessments to identify all applications and services using affected .NET Framework versions, ensuring that proper patching and configuration management procedures are implemented across the entire infrastructure. Regular security monitoring and incident response procedures should be established to detect and respond to potential exploitation attempts. The implementation of web application firewalls and XML security controls can provide additional layers of protection against XXE attacks, while security awareness training for developers can help prevent the introduction of similar vulnerabilities in custom applications.