CVE-2017-6884 in EMG2926
Summary
by MITRE
A command injection vulnerability was discovered on the Zyxel EMG2926 home router with firmware V1.00(AAQT.4)b8. The vulnerability is located in the diagnostic tools, specifically the nslookup function. A malicious user may exploit numerous vectors to execute arbitrary commands on the router, such as the ping_ip parameter to the expert/maintenance/diagnostic/nslookup URI.
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Analysis
by VulDB Data Team • 05/13/2025
The CVE-2017-6884 vulnerability represents a critical command injection flaw in Zyxel EMG2926 home routers running firmware version V1.00(AAQT.4)b8. This vulnerability exists within the router's diagnostic functionality, specifically targeting the nslookup utility that is accessible through the expert/maintenance/diagnostic/nslookup URI endpoint. The flaw allows attackers to inject malicious commands that execute with the privileges of the router's web server process, effectively providing unauthorized remote code execution capabilities. The vulnerability's presence in the diagnostic tools makes it particularly dangerous as these functions are typically intended for network troubleshooting and are often enabled in production environments. The affected device's architecture allows for command injection through the ping_ip parameter, which serves as the primary attack vector for exploiting this weakness. This represents a fundamental failure in input validation and parameter sanitization within the web interface implementation.
The technical exploitation of this vulnerability follows a well-established command injection pattern that aligns with CWE-77 and CWE-88 categories, where user-supplied input is directly incorporated into system commands without proper sanitization. Attackers can leverage the ping_ip parameter to pass malicious command sequences that get executed by the underlying operating system. The router's web server processes these inputs without adequate filtering or escaping mechanisms, creating an environment where arbitrary shell commands can be executed. This type of vulnerability typically stems from improper input validation and the use of dangerous functions like system() or exec() in the application code. The vulnerability's impact is amplified by the fact that it operates at the application layer, requiring no specialized privileges or physical access to the device. The nslookup function, which should only perform DNS resolution, becomes a gateway for complete system compromise through the injection of malicious command sequences.
The operational impact of CVE-2017-6884 extends far beyond simple unauthorized access, as it provides attackers with complete control over the affected router's functionality. Once exploited, attackers can modify network configurations, redirect traffic, establish persistent backdoors, or use the device as a pivot point for attacking other systems within the local network. The vulnerability can be exploited remotely over the internet, making it particularly dangerous for home users who may not be aware of the security implications. This type of attack vector aligns with ATT&CK technique T1059.001 for command and script injection, and T1046 for network service scanning. The compromised device can become part of a botnet, be used for launching attacks against other targets, or serve as a reconnaissance platform for internal network mapping. The vulnerability's presence in a consumer-grade device like the EMG2926 demonstrates how common security flaws can affect widely deployed network infrastructure, potentially creating widespread security issues across multiple households and organizations.
Mitigation strategies for CVE-2017-6884 should focus on immediate firmware updates from Zyxel, as the vendor has released patches addressing this vulnerability. Network administrators should implement network segmentation and access controls to limit the potential impact of compromised devices. The implementation of web application firewalls and input validation rules can help prevent exploitation attempts, while regular security audits of network devices should be conducted to identify similar vulnerabilities. Additionally, disabling unnecessary diagnostic functions and services when not in use provides an additional layer of protection. Organizations should consider implementing network monitoring solutions that can detect anomalous command execution patterns or unusual network traffic originating from compromised devices. The vulnerability highlights the importance of secure coding practices and proper input validation, emphasizing the need for developers to follow security guidelines such as those outlined in the OWASP Top Ten and NIST cybersecurity frameworks. Regular vulnerability assessments and penetration testing should be conducted to identify and remediate similar command injection vulnerabilities in network infrastructure devices.