CVE-2020-3153: Defending Against Cisco AnyConnect Privilege Escalation and DLL Hijacking
Cisco AnyConnect Secure Mobility Client for Windows allows for incorrect handling of directory paths. An attacker with valid credentials on Windows would be able to copy malicious files to arbitrary locations with system level privileges. This could include DLL pre-loading, DLL hijacking, and other related attacks.
FREQUENTLY ASKED
What is CVE-2020-3153 and why does it matter?
CVE-2020-3153 is an Uncontrolled Search Path vulnerability (CWE-427) in the Cisco AnyConnect Secure Mobility Client for Windows installer. It matters because it allows a local, authenticated attacker to copy malicious files to system-level directories. This capability enables attackers to escalate their privileges to SYSTEM level, facilitating persistent access, DLL hijacking, or the deployment of ransomware within an enterprise network.
Which versions of the product are affected?
According to the source data, the vulnerability affects the Cisco AnyConnect Secure Mobility Client for Windows. While the specific version numbers are not explicitly listed in the 'Affected Versions' field of the summary, the vulnerability is inherent to the installer component prior to the remediation patches released by Cisco. Administrators should check their current deployment against the official Cisco advisory.
Has a patch been released for CVE-2020-3153?
Yes, Cisco has released official security updates to address this vulnerability. The remediation involves applying these updates per the vendor's instructions provided in the security advisory. The patch corrects the installer's handling of directory paths, ensuring that file operations cannot be redirected to unauthorized system locations, thereby neutralizing the primary attack vector for DLL pre-loading and hijacking.
What is the remediation deadline and what it means for compliance?
The remediation deadline for CVE-2020-3153 was 2022-11-14. For organizations following CISA's Binding Operational Directive (BOD) 22-01, this deadline represents the date by which federal agencies and associated contractors were required to have the patch fully implemented. Missing this deadline indicates a lapse in mandatory security compliance and increases the risk of exploitation by sophisticated threat actors.
How to check if an instance or deployment is affected?
To determine if a deployment is affected, administrators should verify the version of the Cisco AnyConnect Secure Mobility Client currently installed on Windows endpoints. If the version is older than the patched releases specified in the Cisco Security Advisory (cisco-sa-ac-win-path-traverse-qO4HWBsj), the system is vulnerable. Additionally, security teams can audit the Windows Event Logs for unusual file movement to system directories.
CVE-2020-3153 represents a significant security flaw in the Cisco AnyConnect Secure Mobility Client for Windows, specifically within its installer component. With a CVSS score of 6.5 (Medium severity), this vulnerability involves an uncontrolled search path (CWE-427) that grants local authenticated attackers the ability to escalate privileges to a system level. Given the remediation deadline of 2022-11-14 and its status as a known vulnerability used in ransomware campaigns, immediate patching is mandatory for organizational security and compliance.
Vulnerability Profile Table
Field
Details
CVE ID
CVE-2020-3153
Affected Product & Versions
AnyConnect Secure Mobility Client (Windows)
CVSS Score & Severity
6.5 (MEDIUM)
CVSS Version
3.0
CVSS Vector
CVSS:3.0/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:H/A:N
Attack Vector
LOCAL
Attack Complexity
LOW
Privileges Required
LOW
User Interaction
NONE
CWE IDs
CWE-427
Date Disclosed
2020-02-19
Remediation Deadline
2022-11-14
SSVC Exploitation status
Active
Known Ransomware Use
Yes
EPSS Score & Percentile
0.25087 (96.2%)
Patch Available
Yes
Technical Deep Dive into CWE-427
At the heart of CVE-2020-3153 is CWE-427: Uncontrolled Search Path. In a typical Windows environment, when an application or service attempts to load a resource—most commonly a Dynamic Link Library (DLL)—it follows a specific search order. If the application does not explicitly define the absolute path to the resource, Windows may search through several directories, including the application's working directory and the system's PATH environment variable.
In the case of the Cisco AnyConnect installer, a flaw in how directory paths are handled allows an attacker to manipulate this logic. Specifically, the installer component incorrectly validates the destination of file-copying operations. A local attacker, even with low-level user privileges, can supply a malicious file and trick the AnyConnect service into moving that file into a system-level directory, such as C:\Windows\System32 or other protected program folders.
The Attack Chain
Credential Gain: The attacker must first have valid, albeit low-privileged, credentials on the Windows system.
Staging: The attacker creates a malicious DLL or executable designed to perform unauthorized actions (e.g., creating a new administrator user).
Path Exploitation: By exploiting the AnyConnect installer's path handling logic, the attacker triggers a file copy operation that moves their malicious file into a directory where a high-privilege service is expected to look for a specific DLL.
Execution/Hijacking: When the AnyConnect service or another system process restarts or reaches a specific execution point, it loads the attacker's malicious file instead of the legitimate one. This is known as DLL Hijacking or DLL Pre-loading.
Blast Radius and Surface Area
The attack surface is limited to local users, meaning remote exploitation is not possible without an initial foothold. However, the blast radius is substantial. Once the attacker achieves SYSTEM-level privileges, they have total control over the local machine. This allows for the disabling of antivirus software, the harvesting of credentials from memory (e.g., LSASS), and lateral movement across the internal network. The high EPSS percentile (96.2%) underscores how frequently this vulnerability is targeted in real-world scenarios, particularly as part of multi-stage ransomware attacks.
Who Is Affected
This vulnerability primarily impacts organizations utilizing the Cisco AnyConnect Secure Mobility Client for Windows. This includes remote workers, corporate offices, and any environment where AnyConnect is the primary VPN solution.
Compliance Note: Under CISA’s Binding Operational Directive (BOD) 22-01, this CVE was added to the Known Exploited Vulnerabilities (KEV) catalog. All Federal Civilian Executive Branch (FCEB) agencies were required to remediate this flaw by November 14, 2022. Private sector organizations following NIST or ISO frameworks should view this deadline as a critical benchmark for their own security posturing.
Official Remediation Steps
To mitigate the risks associated with CVE-2020-3153, administrators must follow the official Cisco remediation path:
Inventory Impacted Systems: Identify all Windows endpoints running Cisco AnyConnect. Use an RMM tool or endpoint management software to pull version numbers.
Apply Updates: Deploy the latest AnyConnect installer to all affected endpoints. Ensure the installer package is distributed through a secure channel (e.g., SCCM, InTune, or the AnyConnect head-end auto-update feature).
Verify Patch Success: Post-deployment, audit endpoints to ensure that the version update was successful and that the AnyConnect service is running the corrected code.
Remove Legacy Installers: Ensure that old, vulnerable versions of the installer are removed from shared network drives or local temporary folders to prevent accidental re-installation.
Security Best Practices for Path Management
Beyond patching CVE-2020-3153, organizations should implement the following defensive measures to protect against Uncontrolled Search Path vulnerabilities:
Enforce Safe DLL Search Mode: Ensure that SafeDllSearchMode is enabled via Registry or Group Policy, which forces the system to search the current directory last when loading DLLs.
Strict File Permissions: Restrict write access to system-level directories and application folders. Only the SYSTEM and TrustedInstaller accounts should have write access to critical path locations.
Endpoint Detection and Response (EDR): Utilize EDR tools to monitor for "File Write" events into system directories originating from non-administrative processes.
Application Whitelisting/Control: Implement solutions like Windows Defender Application Control (WDAC) or AppLocker to prevent the execution of unauthorized DLLs, even if they are placed in system directories.
Audit Environment Variables: Regularly scan for user-modified PATH variables that might point to insecure or attacker-controlled directories.
Principle of Least Privilege: Ensure that standard users do not have administrative rights on their local machines, which significantly limits the impact of most local privilege escalation vulnerabilities.