CVE-2017-6638 in AnyConnect Secure Mobility Client
Summary
by MITRE
A vulnerability in how DLL files are loaded with Cisco AnyConnect Secure Mobility Client for Windows could allow an authenticated, local attacker to install and run an executable file with privileges equivalent to the Microsoft Windows SYSTEM account. The vulnerability is due to incomplete input validation of path and file names of a DLL file before it is loaded. An attacker could exploit this vulnerability by creating a malicious DLL file and installing it in a specific system directory. A successful exploit could allow the attacker to execute commands on the underlying Microsoft Windows host with privileges equivalent to the SYSTEM account. The attacker would need valid user credentials to exploit this vulnerability. This vulnerability affects all Cisco AnyConnect Secure Mobility Client for Windows software versions prior to 4.4.02034. Cisco Bug IDs: CSCvc97928.
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Analysis
by VulDB Data Team • 08/25/2024
The vulnerability described in CVE-2017-6638 represents a critical privilege escalation flaw within Cisco AnyConnect Secure Mobility Client for Windows, specifically targeting the dynamic link library (DLL) loading mechanism. This weakness stems from inadequate input validation during the DLL loading process, creating a pathway for authenticated local attackers to execute arbitrary code with SYSTEM-level privileges. The vulnerability exploits the client's failure to properly sanitize and validate file paths and names before executing loaded DLL components, fundamentally undermining the security boundaries of the application.
The technical implementation of this vulnerability leverages Windows DLL loading behavior where the system searches for required libraries in a specific order and directory hierarchy. When Cisco AnyConnect processes certain operations, it loads DLL files without sufficient validation of the file paths or names, allowing an attacker to place a malicious DLL in a directory that will be searched during the loading process. This particular flaw falls under CWE-78, which addresses improper neutralization of special elements used in OS commands, and CWE-22, concerning improper limitation of a pathname to a restricted directory. The vulnerability is particularly dangerous because it operates within the context of an authenticated user session, meaning attackers need valid credentials but can then escalate their privileges to the highest possible level within the Windows operating system.
The operational impact of this vulnerability extends far beyond simple local privilege escalation, as it provides attackers with complete control over the affected Windows host. With SYSTEM-level privileges, an attacker gains access to all system resources, can modify or delete critical files, access encrypted data, and potentially establish persistence mechanisms. The attack vector requires local access and valid user credentials, making it a local privilege escalation vulnerability rather than a remote one, but the severity remains extremely high due to the privilege level achieved. The affected software versions prior to 4.4.02034 represent a broad range of installations, making this vulnerability particularly widespread and dangerous in enterprise environments where Cisco AnyConnect is commonly deployed. The vulnerability aligns with ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation', and T1059, covering 'Command and Scripting Interpreter', as successful exploitation would enable attackers to execute commands with elevated privileges.
Mitigation strategies for this vulnerability focus primarily on immediate software updates to version 4.4.02034 or later, which contains the necessary patches to address the incomplete input validation issue. Organizations should also implement additional security controls including privileged account management, regular security assessments, and monitoring for unusual file creation or modification in system directories. Network segmentation and least privilege principles should be enforced to limit the potential impact of successful exploitation. Security teams should monitor for suspicious DLL loading activities and implement application whitelisting policies to prevent unauthorized DLL execution. The vulnerability demonstrates the critical importance of proper input validation in security-sensitive applications and serves as a reminder of how seemingly minor implementation flaws can lead to significant privilege escalation capabilities within operating systems.