CVE-2024-20492 in TelePresence Video Communication Server (VCS) Expressway
Summary
by MITRE • 10/02/2024
A vulnerability in the restricted shell of Cisco Expressway Series could allow an authenticated, local attacker to perform command injection attacks on the underlying operating system and elevate privileges to root. To exploit this vulnerability, the attacker must have Administrator-level credentials with read-write privileges on an affected device.
This vulnerability is due to insufficient validation of user-supplied input. An attacker could exploit this vulnerability by submitting a series of crafted CLI commands. A successful exploit could allow the attacker to escape the restricted shell and gain root privileges on the underlying operating system of the affected device. Note: Cisco Expressway Series refers to Cisco Expressway Control (Expressway-C) devices and Cisco Expressway Edge (Expressway-E) devices.
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Analysis
by VulDB Data Team • 02/20/2025
This vulnerability resides within the restricted shell environment of Cisco Expressway Series devices, specifically affecting both Cisco Expressway Control and Expressway Edge platforms. The flaw represents a critical privilege escalation vulnerability that fundamentally undermines the security model of these communication appliances. The restricted shell design is intended to limit administrative access to only approved commands while preventing direct system-level interactions, yet this vulnerability creates a pathway for authenticated attackers to bypass these protective measures. The vulnerability stems from inadequate input validation mechanisms within the command processing pipeline of the restricted shell environment.
The technical exploitation mechanism involves crafting specific Command Line Interface commands that manipulate the input validation processes. When an authenticated administrator with read-write privileges submits maliciously formatted CLI inputs, the system fails to properly sanitize or validate these inputs before processing them within the underlying operating system context. This insufficient input validation creates a command injection vector that allows attackers to execute arbitrary commands beyond the intended restricted shell boundaries. The vulnerability specifically targets the shell's parsing and execution logic, where user-supplied input is not adequately filtered or escaped before being interpreted by the system's command processor.
The operational impact of this vulnerability is severe and far-reaching for organizations relying on Cisco Expressway Series devices for their communication infrastructure. Successful exploitation results in complete system compromise with root privileges, enabling attackers to access all system resources, modify critical configurations, exfiltrate sensitive data, and potentially establish persistent backdoors. This privilege escalation capability transforms a local administrative account into a system-level administrator, effectively removing any isolation between legitimate administrative functions and malicious activities. The vulnerability undermines the fundamental security assumptions of the device's architecture and could lead to complete network compromise if these devices are connected to critical infrastructure.
Organizations should implement immediate mitigations including restricting administrative access to only trusted personnel with proper authorization, implementing network segmentation to limit access to these devices, and monitoring for unusual CLI command patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-77 and CWE-78 categories under the Common Weakness Enumeration framework, specifically addressing command injection flaws in input validation. From an ATT&CK framework perspective, this vulnerability maps to T1059.001 (Command and Scripting Interpreter) and T1548.001 (Abuse Elevation Control Mechanism), representing both command execution and privilege escalation techniques. Cisco has released security advisories and patches addressing this vulnerability, and organizations should prioritize applying these updates while maintaining comprehensive monitoring of administrative activities on affected devices.