CVE-2018-20334 in AsusWRT
Summary
by MITRE
An issue was discovered in ASUSWRT 3.0.0.4.384.20308. When processing the /start_apply.htm POST data, there is a command injection issue via shell metacharacters in the fb_email parameter. By using this issue, an attacker can control the router and get shell.
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Analysis
by VulDB Data Team • 04/17/2024
This vulnerability exists within ASUSWRT firmware version 3.0.0.4.384.20308 where the web interface fails to properly sanitize user input when processing POST requests to the /start_apply.htm endpoint. The fb_email parameter specifically lacks adequate input validation and sanitization measures, allowing malicious actors to inject shell metacharacters that get executed within the router's command processing pipeline. This represents a critical command injection flaw that directly violates security principles outlined in CWE-77 and CWE-94, where user-supplied data is improperly incorporated into shell commands without proper escaping or filtering mechanisms.
The technical exploitation of this vulnerability occurs when an attacker submits a malicious payload through the fb_email field in the POST request to /start_apply.htm. The router's web server processes this input without adequate sanitization, allowing shell metacharacters such as semicolons, pipes, or backticks to execute arbitrary commands on the underlying operating system. This command injection vulnerability enables attackers to execute arbitrary shell commands with the privileges of the web server process, which typically runs with elevated permissions on the router. The impact extends beyond simple command execution to full system compromise, as demonstrated by the ability to gain shell access and control the entire router.
The operational impact of this vulnerability is severe and far-reaching within network security contexts. An attacker who successfully exploits this command injection flaw can gain complete control over the affected router, enabling them to modify network configurations, intercept traffic, create backdoors, or use the device as a pivot point for attacking other systems within the local network. This vulnerability directly maps to ATT&CK technique T1059.001 for command and scripting interpreter and T1021.001 for remote services, as it allows for remote command execution and service manipulation. The compromised router can then serve as a persistent foothold for advanced persistent threats or be used in botnet formations for distributed denial-of-service attacks.
Mitigation strategies for this vulnerability require immediate firmware updates from ASUS to address the input sanitization deficiencies in the web interface. Network administrators should also implement network segmentation and access controls to limit exposure of router management interfaces to trusted networks only. Additional defensive measures include disabling unnecessary web management interfaces, implementing intrusion detection systems to monitor for suspicious POST requests, and regularly auditing router configurations. The vulnerability highlights the critical importance of input validation and the principle of least privilege in embedded systems security, as outlined in the OWASP Top Ten and NIST Cybersecurity Framework guidelines. Organizations should also consider implementing network monitoring solutions that can detect anomalous command execution patterns and shell activity originating from router management interfaces.