CVE-2025-20206 is a vulnerability identified in the interprocess communication (IPC) mechanism of Cisco Secure Client for Windows. The root cause is insufficient validation of resources loaded at runtime, specifically related to cryptographic signature verification. This flaw enables an authenticated local attacker to perform a DLL hijacking attack by sending specially crafted IPC messages to a targeted Cisco Secure Client process. The hijacked DLL can then execute arbitrary code with SYSTEM-level privileges, effectively allowing full control over the affected device. The vulnerability is contingent on the presence of the Secure Firewall Posture Engine component, which is part of the Cisco Secure Client installation. A wide range of Cisco Secure Client versions, spanning from 4.9.x to 5.1.x, are affected. Exploitation requires valid user credentials on the Windows system but does not require user interaction beyond authentication. The CVSS v3.1 base score is 7.1, reflecting high severity due to the high impact on confidentiality and integrity, moderate attack complexity, and the requirement for local privileges. No public exploits have been reported yet, but the vulnerability poses a serious risk in environments where Cisco Secure Client is deployed, especially in enterprise settings where endpoint security is critical.

The vulnerability allows an authenticated local attacker to escalate privileges to SYSTEM level, which can lead to full compromise of the affected Windows machine. This includes unauthorized access to sensitive data, manipulation or deletion of critical files, installation of persistent malware, and potential lateral movement within a network. Since Cisco Secure Client is widely used in enterprise environments for secure VPN and endpoint posture enforcement, exploitation could undermine network security and trust. The impact is particularly severe in organizations with high-value assets, regulated data, or critical infrastructure. The requirement for local authentication limits remote exploitation but insider threats or compromised user accounts could leverage this vulnerability to gain elevated privileges. The absence of known exploits in the wild currently reduces immediate risk but does not diminish the urgency for remediation given the potential damage.

Organizations should immediately verify if they are running affected versions of Cisco Secure Client with the Secure Firewall Posture Engine installed. Cisco should be consulted for official patches or updates addressing this vulnerability; applying these updates promptly is the most effective mitigation. If patches are not yet available, consider disabling or uninstalling the Secure Firewall Posture Engine component temporarily to reduce attack surface. Implement strict access controls and monitoring on endpoints to detect unusual IPC activity or DLL loading behavior. Employ application whitelisting and integrity monitoring tools to prevent unauthorized DLL execution. Enforce strong authentication and limit local user privileges to reduce the risk of exploitation by compromised accounts. Regularly audit and review endpoint security configurations and logs for signs of suspicious activity related to IPC channels. Finally, educate users about the risks of credential compromise and enforce multi-factor authentication to minimize the chance of unauthorized local access.