CVE-2020-3556 in AnyConnect Secure Mobility Client
Summary
by MITRE • 11/07/2020
A vulnerability in the interprocess communication (IPC) channel of Cisco AnyConnect Secure Mobility Client Software could allow an authenticated, local attacker to cause a targeted AnyConnect user to execute a malicious script. The vulnerability is due to a lack of authentication to the IPC listener. An attacker could exploit this vulnerability by sending crafted IPC messages to the AnyConnect client IPC listener. A successful exploit could allow an attacker to cause the targeted AnyConnect user to execute a script. This script would execute with the privileges of the targeted AnyConnect user. In order to successfully exploit this vulnerability, there must be an ongoing AnyConnect session by the targeted user at the time of the attack. To exploit this vulnerability, the attacker would also need valid user credentials on the system upon which the AnyConnect client is being run. Cisco has not released software updates that address this vulnerability.
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Analysis
by VulDB Data Team • 12/03/2020
The vulnerability identified as CVE-2020-3556 resides within the interprocess communication mechanisms of Cisco AnyConnect Secure Mobility Client Software, representing a critical security flaw that undermines the integrity of the client's communication channels. This issue manifests as a failure in authentication protocols within the IPC listener component, creating an exploitable entry point for malicious actors who possess valid user credentials on the target system. The vulnerability specifically affects the authentication mechanisms that govern how the AnyConnect client processes incoming communication messages, leaving the IPC channel accessible to unauthorized script execution commands without proper verification of the sender's identity.
The technical exploitation of this vulnerability requires an attacker to leverage an active AnyConnect session on the target system while maintaining valid user credentials, demonstrating that the flaw operates within the context of an already compromised user environment. The lack of authentication to the IPC listener means that malicious IPC messages can be sent directly to the AnyConnect client's communication interface without requiring additional authorization steps. This design flaw enables an authenticated local attacker to craft and transmit specially crafted IPC messages that trigger unintended script execution within the context of the targeted user's session, effectively bypassing normal security boundaries that would typically prevent such unauthorized operations.
The operational impact of CVE-2020-3556 extends beyond simple privilege escalation, as it provides attackers with a method to execute arbitrary code with the privileges of the targeted AnyConnect user, potentially enabling further lateral movement within the network or access to sensitive corporate resources. The requirement for an ongoing AnyConnect session means that the vulnerability cannot be exploited passively, but rather requires active engagement with the target user's active connection, making it more difficult to exploit at scale but no less dangerous when successfully targeted. This vulnerability directly relates to CWE-284, which describes inadequate access control mechanisms, and aligns with ATT&CK techniques involving privilege escalation and persistent threats through legitimate system processes. The lack of official software updates from Cisco at the time of disclosure meant that organizations had to rely on temporary mitigations and monitoring solutions to protect against potential exploitation attempts.
Organizations affected by this vulnerability should implement immediate security controls including network segmentation to limit access to AnyConnect client systems, enhanced monitoring of IPC communication patterns, and regular security assessments of client endpoints. The absence of vendor patches necessitated the deployment of additional security layers such as application control policies and endpoint detection mechanisms to identify and prevent unauthorized IPC message transmission. This vulnerability highlights the critical importance of proper authentication mechanisms in IPC channels and serves as a reminder of the potential for privilege escalation through seemingly benign communication interfaces. The security community should consider this issue when evaluating the security posture of remote access solutions and implementing defense-in-depth strategies that protect against both external and internal threats within corporate networks.