CVE-2020-3433

What is Cisco AnyConnect Secure Mobility Client?

AnyConnect is Cisco's VPN client software, installed on end-user Windows machines to establish encrypted connections back to an organization's network. Because VPN client software typically runs components with elevated privileges to manage network interfaces, a local privilege-escalation bug in it lets any user already logged into the machine — even with no special access — become a full SYSTEM-level administrator.

Overview

CVE-2020-3433 is a DLL hijacking vulnerability (CWE-427, uncontrolled search path element) in AnyConnect's interprocess communication (IPC) channel on Windows. A locally authenticated attacker — any standard, low-privileged user already logged into the Windows machine — can exploit insufficient validation of resources loaded at runtime to have the AnyConnect service load a malicious DLL, executing code with SYSTEM privileges (CVSS 3.1: AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H, 7.8 High).

Technical Details

DLL hijacking occurs when an application loads a library from a path an attacker can write to, without adequately restricting where that library search happens. In AnyConnect's case, its IPC-related component doesn't sufficiently validate the resources it loads at runtime, allowing a locally-planted malicious DLL to be loaded and executed in the context of the AnyConnect service — which, because VPN clients typically run with SYSTEM privileges to manage network configuration, hands the attacker complete control of the machine.

Discovery

Fixed by Cisco as part of its routine security advisory process for AnyConnect.

Exploitation Context

This CVE's ransomwareUse: true flag on this site reflects confirmed use of the vulnerability by ransomware operators as part of post-compromise privilege escalation — a common pattern where an attacker who has already gained initial low-privilege access to a Windows endpoint (via phishing, credential theft, or another vector) uses a local privilege-escalation bug like this one to reach SYSTEM and deploy ransomware with maximum impact.

Remediation

1. Update Cisco AnyConnect Secure Mobility Client for Windows to the fixed version specified in Cisco's advisory immediately.
2. Restrict local administrative rights for standard users where possible, reducing the population of accounts that could exploit a local privilege-escalation bug like this one.
3. Deploy endpoint detection capable of identifying DLL side-loading and hijacking techniques, given this vulnerability's confirmed use in ransomware intrusion chains.
4. Treat any endpoint where AnyConnect remained unpatched as a higher-priority target for compromise assessment, particularly if other signs of intrusion (phishing clicks, credential compromise) are present.