CVE-2021-1237 in AnyConnect Secure Mobility Client
Summary
by MITRE • 01/14/2021
A vulnerability in the Network Access Manager and Web Security Agent components of Cisco AnyConnect Secure Mobility Client for Windows could allow an authenticated, local attacker to perform a DLL injection attack. To exploit this vulnerability, the attacker would need to have valid credentials on the Windows system. The vulnerability is due to insufficient validation of resources that are loaded by the application at run time. An attacker could exploit this vulnerability by inserting a configuration file in a specific path in the system which, in turn, causes a malicious DLL file to be loaded when the application starts. A successful exploit could allow the attacker to execute arbitrary code on the affected machine with SYSTEM privileges.
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Analysis
by VulDB Data Team • 02/14/2021
This vulnerability resides within Cisco AnyConnect Secure Mobility Client's Network Access Manager and Web Security Agent components for Windows systems, representing a critical security flaw that enables local privilege escalation through DLL injection techniques. The vulnerability stems from inadequate resource validation mechanisms within the application's runtime environment, specifically failing to properly verify the authenticity and integrity of dynamically loaded libraries. According to CWE-426, this weakness falls under the category of Untrusted Search Path, where the application searches for required libraries in predictable locations without sufficient validation of their source. The attack vector requires an authenticated local user with valid system credentials, making it a local privilege escalation vulnerability that leverages the trust model of the application's loading mechanism.
The technical exploitation process involves a sophisticated attack chain where the authenticated attacker places a malicious configuration file in a predetermined system path that the vulnerable application monitors during startup. This configuration file acts as a trigger mechanism that causes the application to load a malicious dynamic link library from an untrusted location. The vulnerability's design flaw allows the application to load DLLs from locations outside its intended secure search paths, creating an injection point that bypasses normal security controls. When the application launches, it automatically loads the malicious DLL without proper validation, enabling code execution with elevated privileges. This behavior aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter, as the malicious code execution occurs through legitimate application loading mechanisms rather than direct system calls.
The operational impact of this vulnerability extends beyond simple code execution, as successful exploitation grants attackers SYSTEM privileges on the compromised machine, effectively providing complete control over the affected system. This privilege escalation capability allows attackers to bypass traditional security controls, access sensitive data, modify system configurations, and establish persistent access through various persistence mechanisms. The vulnerability affects all versions of Cisco AnyConnect Secure Mobility Client for Windows that include the affected components, making it particularly concerning for enterprise environments where these clients are widely deployed. Organizations running these clients are vulnerable to sophisticated attacks that could compromise entire network infrastructures, especially when the compromised systems have elevated privileges or access to sensitive network resources.
Mitigation strategies should focus on immediate patch deployment from Cisco, which addresses the root cause by implementing proper resource validation and secure library loading mechanisms. System administrators should also implement additional security controls such as restricting write access to application directories and monitoring for unauthorized file modifications in critical system paths. The principle of least privilege should be enforced by ensuring that users only have necessary permissions to perform their duties, reducing the attack surface for local exploitation attempts. Network segmentation and monitoring solutions should be deployed to detect suspicious file creation activities in application directories, particularly around startup processes. Organizations should also consider implementing application whitelisting policies that restrict which DLLs can be loaded by the AnyConnect client, providing an additional layer of defense against unauthorized code injection attempts. Regular security assessments and vulnerability scanning should be conducted to identify similar weaknesses in other applications and ensure comprehensive protection against similar attack vectors.