CVE-2021-20144 in Tower Router
Summary
by MITRE • 12/09/2021
An unauthenticated command injection vulnerability exists in the parameters of operation 49 in the controller_server service on Gryphon Tower routers. An unauthenticated remote attacker on the same network can execute commands as root on the device by sending a specially crafted malicious packet to the controller_server service on port 9999.
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Analysis
by VulDB Data Team • 12/15/2021
This vulnerability represents a critical command injection flaw in the controller_server service of Gryphon Tower routers, specifically affecting operation 49 within the parameter handling mechanism. The vulnerability exists at the application layer where user-supplied input is improperly validated and directly incorporated into system commands without adequate sanitization or escaping mechanisms. This type of flaw falls under the CWE-77 category, which encompasses command injection vulnerabilities where attacker-controlled data is passed to system execution functions. The vulnerability is particularly dangerous because it allows unauthenticated remote code execution, meaning any attacker on the same network segment can exploit this weakness without requiring prior authentication credentials. The affected service operates on port 9999, making it accessible to any device within the local network that can reach this specific port. This attack vector aligns with the ATT&CK technique T1059.001 for command and script injection, where adversaries leverage vulnerabilities to execute malicious commands on target systems.
The technical implementation of this vulnerability stems from insufficient input validation within the controller_server service's parameter parsing logic for operation 49. When legitimate users or attackers send packets containing maliciously crafted parameters to the service, the system fails to properly sanitize or escape these inputs before incorporating them into system commands. This allows attackers to inject arbitrary commands that are then executed with the highest privileges available to the service, which in this case are root privileges. The root-level execution capability means that successful exploitation provides complete system compromise, enabling attackers to gain full control over the router's functionality, access all stored data, modify network configurations, and potentially use the compromised device as a pivot point for further attacks within the network. The vulnerability's impact is amplified by the fact that no authentication is required, making it particularly attractive to threat actors who may already have network access through other means such as compromised credentials or network reconnaissance.
The operational implications of this vulnerability extend beyond simple remote code execution to encompass significant network security risks. Compromised Gryphon Tower routers can serve as persistent backdoors within corporate or residential networks, allowing attackers to maintain long-term access while evading detection. The vulnerability's presence on port 9999, a non-standard port, may initially mask the attack from basic network monitoring tools that focus on common service ports. Network defenders may not immediately recognize the attack traffic as malicious due to the unusual port usage and the legitimate nature of the controller_server service. This vulnerability can be exploited as part of a broader attack chain, potentially enabling lateral movement within networks, data exfiltration, or the establishment of command and control channels. The attack requires only network-level access, making it particularly concerning for environments where physical network security is inadequate or where network segmentation is not properly implemented. Security professionals should consider this vulnerability as a potential indicator of broader network compromise, especially in environments where these routers are deployed without proper network monitoring or intrusion detection measures.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security improvements. The most effective immediate solution is to apply vendor-provided security patches or firmware updates that address the command injection flaw in the controller_server service. Organizations should also implement network segmentation to isolate critical infrastructure from general network access, particularly preventing unnecessary access to port 9999. Network monitoring should be enhanced to detect unusual traffic patterns on non-standard ports, including traffic that may contain command injection payloads. Access control measures should be implemented to restrict which devices can communicate with the controller_server service, potentially through firewall rules or network access control lists. Regular network scanning should be conducted to identify all instances of Gryphon Tower routers and verify that they are running patched firmware versions. Additionally, network defenders should implement behavioral monitoring to detect anomalous command execution patterns that may indicate exploitation attempts. The vulnerability underscores the importance of input validation and proper sanitization of all user-supplied data, which should be implemented as a fundamental security practice across all network services. Organizations should also consider implementing network intrusion prevention systems that can detect and block known command injection patterns in real-time.