CVE-2018-3955 in E1200
Summary
by MITRE
An exploitable operating system command injection exists in the Linksys ESeries line of routers (Linksys E1200 Firmware Version 2.0.09 and Linksys E2500 Firmware Version 3.0.04). Specially crafted entries to network configuration information can cause execution of arbitrary system commands, resulting in full control of the device. An attacker can send an authenticated HTTP request to trigger this vulnerability. Data entered into the 'Domain Name' input field through the web portal is submitted to apply.cgi as the value to the 'wan_domain' POST parameter. The wan_domain data goes through the nvram_set process described above. 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 vulnerability described in CVE-2018-3955 represents a critical operating system command injection flaw affecting Linksys ESeries routers, specifically the E1200 and E2500 models with particular firmware versions. This vulnerability resides within the web-based administrative interface of these networking devices, creating a significant security risk that allows remote attackers to execute arbitrary system commands with complete device control. The flaw stems from inadequate input validation and sanitization within the router's configuration processing pipeline, where user-supplied data flows directly into system command execution contexts without proper security controls.
The technical implementation of this vulnerability occurs through the manipulation of the 'Domain Name' input field within the web portal interface. When administrators or authenticated users enter data into this field, the information is transmitted via HTTP POST requests to the apply.cgi script with the wan_domain parameter. This data then passes through the nvram_set process, which serves as a bridge between the web interface and the underlying system configuration. The critical flaw manifests when the preinit binary receives a SIGHUP signal, triggering execution of the set_host_domain_name function within the libshared.so shared object library, creating an execution path where user input directly influences system command invocation.
This vulnerability aligns with CWE-77 and CWE-88 within the Common Weakness Enumeration framework, specifically categorizing as a command injection vulnerability that allows arbitrary code execution. The ATT&CK framework would classify this under T1059.001 for Command and Scripting Interpreter with specific emphasis on the execution of system commands through web interfaces. The attack vector requires authenticated access to the web administration interface, making it particularly dangerous in environments where administrative credentials are compromised or where default credentials remain unchanged. The impact extends beyond simple privilege escalation to full system compromise, allowing attackers to modify router configurations, install malicious software, redirect network traffic, or establish persistent backdoors.
The operational impact of CVE-2018-3955 is severe and multifaceted, potentially enabling attackers to gain complete control over network infrastructure. Once exploited, attackers can manipulate routing tables, redirect traffic to malicious servers, disable security features, or use the compromised router as a pivot point for attacking internal network resources. The vulnerability affects not just individual devices but entire network segments, as routers serve as critical gateway points. Organizations may experience data exfiltration, network disruption, or the establishment of persistent command and control channels. The authentication requirement does not prevent exploitation in environments where default credentials are used or where administrative sessions are compromised through other attack vectors. Mitigation strategies include immediate firmware updates from Linksys, implementation of network segmentation, monitoring for suspicious administrative activity, and disabling unnecessary web administration interfaces when not required for operational purposes.