CVE-2020-3153: Cisco AnyConnect Secure Mobility Client for Windows Uncontrolled Search Path Vulnerability

CVE-2020-3153 is an uncontrolled search path vulnerability in Cisco AnyConnect Secure Mobility Client for Windows. It stems from incorrect handling of directory paths, allowing an attacker who already has valid credentials on a Windows system to copy malicious files to arbitrary locations with system-level privileges. This can enable DLL pre-loading, DLL hijacking, and similar attacks that escalate privileges or execute code under elevated rights. The issue matters because it has been associated with ransomware use, turning a local foothold into broader system compromise if left unaddressed.

Defenders should treat this as a privilege-escalation risk on endpoints running the client. Confirm all version, configuration, and fix details against the vendor advisory, as public records focus on the weakness class rather than exhaustive product matrices.

How it works

The flaw is classified as CWE-427 (Uncontrolled Search Path Element). Cisco AnyConnect Secure Mobility Client for Windows mishandles directory paths during operations that involve loading or resolving files. An attacker who already possesses valid credentials on the Windows host can place malicious files into locations the client will search or write to. Because those operations can run with system-level privileges, the attacker gains the ability to drop or overwrite files that the client or related processes will load, including DLLs.

In practice this supports classic DLL pre-loading or hijacking techniques: the attacker supplies a malicious library that is found before a legitimate one, or writes files into privileged paths that the software trusts. No remote unauthenticated exploit path is described; the prerequisite is local access with valid credentials. Exact search-order mechanics and trigger conditions must be confirmed against the vendor advisory rather than assumed.

Am I affected? How to find it in your systems

The vulnerability affects Cisco AnyConnect Secure Mobility Client for Windows. This software typically runs on Windows endpoints used for remote access or VPN connectivity—laptops, desktops, and sometimes virtual desktops in enterprise environments. Inventory every Windows system that has the AnyConnect client installed; common locations include Program Files directories and user profile paths associated with Cisco VPN software.

• Use software inventory tools, SCCM/Intune reports, or package managers to list installed Cisco AnyConnect versions and components.
• Compare installed builds against the versions listed as fixed in the vendor advisory; do not rely on version numbers not present in that advisory.
• Review configurations that involve custom install paths, auto-updates, or elevated service accounts, as these can influence path-handling behavior.
• Look for telemetry or endpoint-detection alerts involving unexpected file writes to system directories, DLL loads from non-standard locations, or privilege escalations coinciding with AnyConnect process activity. Windows event logs for process creation, file creation, and module loads can surface suspicious activity after the fact.

If the client is not present, the host is not affected by this specific CVE. Confirm scope with the vendor advisory before declaring systems clean.

How to remediate

Patch first. Apply the updates published by Cisco for Cisco AnyConnect Secure Mobility Client for Windows, following the vendor instructions exactly as stated in the advisory. CISA’s required action is to apply those updates per vendor guidance. After installation, verify the new build is running and that the client functions normally.

Once patched, harden against the broader uncontrolled-search-path class:

• Ensure installation and working directories for the client are writable only by administrators.
• Remove unnecessary write permissions from paths that AnyConnect or its services may search.
• Prefer application control or allow-listing that blocks untrusted DLLs from loading into privileged processes.
• Keep endpoint detection and response (EDR) rules tuned for DLL hijacking and unexpected system-level file drops.

Re-inventory after remediation to confirm no residual vulnerable installations remain.

If you can't patch immediately

Until the vendor update can be applied, reduce exposure with compensating controls focused on the local privilege-escalation nature of the issue:

• Segment systems running AnyConnect so that a compromised endpoint has limited ability to reach high-value assets or domain controllers.
• Enforce least-privilege for interactive users; avoid granting local admin rights where possible, since the attack already requires valid credentials.
• Deploy or tighten application control policies that prevent unauthorized DLLs from loading into AnyConnect or system processes.
• Increase monitoring and alerting on file-creation events in system directories, unexpected module loads, and AnyConnect process behavior that could indicate path abuse.
• If the client’s elevated features can be temporarily restricted or the software can be disabled on non-essential hosts without breaking operations, do so until the patch is installed.

Virtual patching or network WAF rules offer limited value here because the vulnerability is local to the Windows client. Prioritize rapid patching over long-term work-arounds.

If your data may have been exposed

Actively exploited vulnerabilities, especially those with known ransomware use, frequently lead to broader breaches once an attacker obtains elevated privileges. If you suspect exploitation—unusual file drops, ransomware indicators, or lateral movement after AnyConnect activity—treat the incident as a potential compromise: isolate affected hosts, preserve forensic evidence, and follow your incident-response plan. Review whether credentials or data accessible from those systems could have been accessed. You can run a free exposure scan of your email addresses against known breach data to determine whether associated accounts appear in public breach corpora and then force password resets or enable stronger authentication where needed.