CVE-2018-17208 in Velop
Summary
by MITRE
Linksys Velop 1.1.2.187020 devices allow unauthenticated command injection, providing an attacker with full root access, via cgi-bin/zbtest.cgi or cgi-bin/zbtest2.cgi (scripts that can be discovered with binwalk on the firmware, but are not visible in the web interface). This occurs because shell metacharacters in the query string are mishandled by ShellExecute, as demonstrated by the zbtest.cgi?cmd=level&level= substring. This can also be exploited via CSRF.
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Analysis
by VulDB Data Team • 03/25/2020
The vulnerability identified as CVE-2018-17208 affects Linksys Velop mesh networking systems running firmware version 1.1.2.187020 and potentially earlier versions. This critical security flaw represents a command injection vulnerability that allows unauthenticated attackers to execute arbitrary commands with root privileges on affected devices. The vulnerability stems from improper input validation within the web application's handling of HTTP request parameters, specifically within the zbtest.cgi and zbtest2.cgi scripts that are embedded within the device firmware. These scripts are not exposed through the standard web interface but can be discovered through firmware analysis using tools like binwalk, making them accessible to attackers who possess basic firmware examination capabilities.
The technical exploitation mechanism involves the mishandling of shell metacharacters within the query string parameters of HTTP requests sent to the affected cgi-bin scripts. When an attacker crafts a malicious request containing shell metacharacters in the command parameter, the ShellExecute function fails to properly sanitize or escape these inputs, leading to arbitrary command execution. The specific example demonstrates how the zbtest.cgi?cmd=level&level= parameter structure can be manipulated to inject shell commands, while the CSRF vulnerability aspect indicates that attackers can leverage cross-site request forgery techniques to execute commands without requiring direct user interaction. This vulnerability directly maps to CWE-77 which describes improper neutralization of special elements used in a command inside a web application, and also aligns with CWE-94 which covers improper execution of code due to inadequate input sanitization.
The operational impact of this vulnerability is severe and far-reaching, as it provides complete system compromise without requiring authentication or user interaction. An attacker with access to the network can gain root-level control over the affected devices, enabling them to modify network configurations, install malicious software, redirect traffic, or use the compromised devices as entry points for further attacks within the network infrastructure. The vulnerability affects not just individual devices but entire mesh network deployments, potentially allowing attackers to establish persistent backdoors or use compromised nodes as part of larger attack campaigns. The fact that these scripts are hidden within firmware rather than exposed through the web interface means that traditional web application firewalls or security scanning tools may not detect their presence, making the vulnerability particularly dangerous for network administrators who rely on standard security controls.
Mitigation strategies for this vulnerability should include immediate firmware updates from Linksys to address the command injection flaw, proper network segmentation to limit access to these devices, and implementation of network monitoring to detect unusual command execution patterns. Organizations should also consider disabling unnecessary cgi-bin scripts or implementing web application firewalls to filter malicious requests before they reach the vulnerable components. The vulnerability demonstrates the importance of proper input validation and output encoding in web applications, particularly in embedded systems where traditional security controls may be insufficient. From an ATT&CK perspective, this vulnerability maps to T1059.001 for command and scripting interpreter and T1068 for exploit for privilege escalation, highlighting the need for comprehensive network security controls that address both external and internal threats in IoT environments.