CVE-2018-3954 in E1200
Summary
by MITRE
Devices in the Linksys ESeries line of routers (Linksys E1200 Firmware Version 2.0.09 and Linksys E2500 Firmware Version 3.0.04) are susceptible to OS command injection vulnerabilities due to improper filtering of data passed to and retrieved from NVRAMData entered into the 'Router Name' input field through the web portal is submitted to apply.cgi as the value to the 'machine_name' POST parameter. When the 'preinit' binary receives the SIGHUP signal it enters a code path that calls a function named 'set_host_domain_name' from its libshared.so shared object.
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Analysis
by VulDB Data Team • 05/30/2023
The CVE-2018-3954 vulnerability affects Linksys E1200 and E2500 routers running specific firmware versions, presenting a critical operating system command injection flaw that allows remote attackers to execute arbitrary commands on the affected devices. This vulnerability stems from insufficient input validation within the web administration interface, specifically in how the 'Router Name' field processes user-supplied data. The flaw manifests when a malicious actor submits specially crafted input through the web portal interface, which is then passed to the apply.cgi script as the machine_name POST parameter. The vulnerability is particularly concerning as it operates at the system level, potentially enabling full device compromise and unauthorized access to network resources.
The technical exploitation occurs through a specific code path within the preinit binary that handles the SIGHUP signal, which triggers the set_host_domain_name function from the libshared.so shared object. This function fails to properly sanitize or filter input data retrieved from NVRAMData, creating a direct injection vector for OS commands. The vulnerability is classified as a command injection flaw, which maps to CWE-77 in the Common Weakness Enumeration catalog, representing one of the most dangerous classes of vulnerabilities in network devices due to its potential for remote code execution. The attack vector is particularly dangerous because it requires no authentication, making it accessible to any remote user who can access the web interface.
The operational impact of this vulnerability extends far beyond simple command execution, as it allows attackers to gain complete control over the affected routers and potentially compromise the entire network infrastructure they protect. An attacker could use this vulnerability to install malicious firmware, redirect network traffic, create backdoors, or access sensitive network data. The preinit binary's handling of the SIGHUP signal creates a persistent attack surface that could be exploited multiple times during device operation, making this vulnerability particularly dangerous for network administrators who may not immediately detect such attacks. This type of vulnerability aligns with ATT&CK technique T1059.001, which describes the use of command and scripting interpreters for execution, and T1021.001, which covers remote services such as web services.
Mitigation strategies for CVE-2018-3954 should prioritize immediate firmware updates from Linksys, as the vendor has released patches addressing this specific vulnerability. Network administrators should implement strict network segmentation to limit access to router administration interfaces, restricting access to authorized personnel only through secure VPN connections or dedicated management networks. Additional protective measures include disabling unnecessary services, implementing web application firewalls to filter malicious input, and conducting regular security audits of network infrastructure. The vulnerability highlights the importance of input validation and proper sanitization of user-supplied data, principles that should be integrated into all network device development processes. Organizations should also consider network monitoring solutions that can detect anomalous behavior patterns indicative of command injection attempts, as these attacks may not always result in immediate system compromise but could establish persistent access to network resources.