CVE-2011-2039 in AnyConnect Secure Mobility Client
Summary
by MITRE
The helper application in Cisco AnyConnect Secure Mobility Client (formerly AnyConnect VPN Client) before 2.3.185 on Windows, and on Windows Mobile, downloads a client executable file (vpndownloader.exe) without verifying its authenticity, which allows remote attackers to execute arbitrary code via the url property to a certain ActiveX control in vpnweb.ocx, aka Bug ID CSCsy00904.
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Analysis
by VulDB Data Team • 12/02/2024
The vulnerability described in CVE-2011-2039 represents a critical security flaw in Cisco AnyConnect Secure Mobility Client versions prior to 2.3.185 on Windows and Windows Mobile platforms. This issue stems from a dangerous trust model within the client's helper application that fails to validate the authenticity of downloaded executable files, creating an exploitable condition that remote attackers can leverage for arbitrary code execution. The vulnerability specifically affects the vpndownloader.exe component that is downloaded as part of the VPN connection process, making it a significant concern for organizations relying on Cisco's VPN solutions for secure remote access.
The technical implementation of this vulnerability occurs through the ActiveX control vpnweb.ocx which exposes a url property that can be manipulated by remote attackers. When an attacker crafts a malicious URL and passes it through this vulnerable ActiveX interface, the helper application automatically downloads the specified executable file without performing any cryptographic verification or integrity checks. This design flaw aligns with CWE-502, which categorizes insecure deserialization and improper input validation as primary contributors to such attacks, and represents a classic example of insecure download handling that violates fundamental security principles of input sanitization and validation.
The operational impact of this vulnerability extends beyond simple code execution to encompass complete system compromise and potential data exfiltration. Attackers can leverage this vulnerability to download and execute malicious payloads that may include keyloggers, backdoors, or additional malware components that can persist on the victim's system. The attack surface is particularly concerning for enterprise environments where the AnyConnect client is widely deployed, as successful exploitation could provide attackers with persistent access to corporate networks, potentially enabling lateral movement and privilege escalation attacks. This vulnerability also maps to ATT&CK technique T1190, which covers exploitation of remote services through the use of malicious files, and T1059, which involves the execution of malicious code through various system interfaces.
Mitigation strategies for CVE-2011-2039 should prioritize immediate patch deployment to upgrade to Cisco AnyConnect Secure Mobility Client version 2.3.185 or later, which implements proper executable verification mechanisms. Organizations should also implement network-level controls such as web filtering and proxy configurations that can block or inspect traffic to known malicious domains that might be used in exploitation attempts. Additionally, security administrators should consider disabling ActiveX controls in browser environments where the AnyConnect client is not required, and implement application whitelisting policies that restrict execution of unknown or unverified executables. The vulnerability demonstrates the critical importance of secure coding practices around file handling and the necessity of implementing proper cryptographic verification mechanisms before executing downloaded content, principles that align with NIST SP 800-160 and ISO 27001 security framework requirements for secure software development practices.