CVE-2017-0248 in .NET Framework
Summary
by MITRE
Microsoft .NET Framework 2.0, 3.5, 3.5.1, 4.5.2, 4.6, 4.6.1, 4.6.2 and 4.7 allow an attacker to bypass Enhanced Security Usage taggings when they present a certificate that is invalid for a specific use, aka ".NET Security Feature Bypass Vulnerability."
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Analysis
by VulDB Data Team • 12/22/2020
The vulnerability identified as CVE-2017-0248 represents a critical security flaw in Microsoft .NET Framework versions 2.0 through 4.7 that undermines the enhanced security mechanisms designed to prevent improper certificate usage. This issue specifically targets the certificate validation process within the .NET Framework, where the system fails to properly enforce Enhanced Security Usage (ESU) taggings that should restrict certificate applications to their intended purposes. The flaw allows attackers to circumvent security controls by presenting certificates that are technically invalid for specific security uses yet still gain access to restricted functionality.
The technical root cause of this vulnerability stems from insufficient certificate validation logic within the .NET Framework's security subsystem. When certificates are processed, the framework should verify that each certificate meets the enhanced security usage requirements specified in the Enhanced Security Usage taggings. However, the implementation contains a gap where certificates with invalid usage attributes can still pass validation checks under certain conditions, effectively bypassing the intended security boundaries. This behavior violates the fundamental security principle of least privilege and certificate-based access control that should prevent unauthorized certificate usage.
The operational impact of this vulnerability is significant as it enables attackers to perform privilege escalation and access restricted resources that should be protected by certificate-based security policies. An attacker could leverage this bypass to execute malicious code with elevated privileges, access sensitive data, or perform unauthorized operations within systems that rely on .NET Framework security controls. The vulnerability affects a broad range of Microsoft .NET Framework versions, making it particularly dangerous as organizations with legacy systems using older framework versions remain exposed to this attack vector.
Security professionals should consider this vulnerability in the context of the CWE-284 access control weakness classification, where improper access control allows unauthorized users to access protected resources. The vulnerability also aligns with ATT&CK technique T1552.001, which involves the use of certificates for privilege escalation and access control bypass. Organizations should implement immediate mitigations including applying Microsoft security updates, reviewing certificate policies, and monitoring for suspicious certificate usage patterns. Additionally, administrators should consider implementing certificate-based access controls outside the .NET Framework to provide additional layers of protection against this specific bypass mechanism.
The vulnerability demonstrates the importance of proper certificate validation mechanisms in security-critical frameworks and highlights the need for comprehensive security testing of cryptographic implementations. Organizations should conduct thorough assessments of their .NET Framework deployments to identify systems potentially affected by this vulnerability and ensure proper patch management procedures are in place to address similar issues in the future. This flaw serves as a reminder of the critical nature of certificate validation in maintaining system security boundaries and preventing unauthorized access to protected resources.