CVE-2026-91853 in X5000R
Summary
by MITRE • 09/15/2026
A vulnerability has been found in TOTOLINK X5000R 9.1.0cu.2089_B20211224. The impacted element is the function exportOvpn of the file /cgi-bin/cstecgi.cgi?action=exportOvpn&type=user of the component Export Ovpn Handler. The manipulation of the argument filetype leads to os command injection. The attack can be initiated remotely. The exploit has been disclosed to the public and may be used.
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Analysis
by VulDB Data Team • 09/15/2026
The vulnerability identified in TOTOLINK X5000R firmware version 9.1.0cu.2089_B20211224 represents a critical security flaw within the device's web management interface, specifically affecting the OpenVPN configuration export functionality. This component is responsible for generating and delivering VPN profile files to authorized users, allowing them to connect their devices securely to private networks managed by the router. The core of the issue resides in the cgi-bin/cstecgi.cgi script, which serves as the primary gateway for handling various administrative requests via HTTP GET or POST parameters. When a user initiates an export request with the action parameter set to exportOvpn and specifies a type of user, the backend logic processes this input to construct the appropriate configuration file content. However, the implementation fails to adequately sanitize or validate the filetype argument before passing it to underlying system commands for processing.
This lack of proper input validation results in an operating system command injection vulnerability, classified under CWE-78: Improper Neutralization of Special Elements used in an OS Command. The attacker can manipulate the filetype parameter by injecting shell metacharacters such as semicolons or ampersands to append arbitrary commands to the legitimate execution flow. Because this function is accessible through the web interface and does not require complex authentication bypasses beyond standard administrative credentials, it presents a significant risk vector for remote exploitation. The vulnerability allows an authenticated attacker to execute system-level commands with the privileges of the web server process, which typically runs under elevated permissions on embedded Linux devices like routers.
The operational impact of this command injection is severe, as it effectively grants full control over the compromised router's operating system. An adversary can leverage this access to read sensitive configuration files containing plaintext passwords or cryptographic keys, modify network routing tables to facilitate man-in-the-middle attacks, install persistent backdoors for long-term surveillance, or pivot into other devices on the local area network. Since the exploit has been publicly disclosed and is known to be functional, automated scanning tools and opportunistic attackers are actively targeting vulnerable instances across the internet. This widespread availability of working exploits significantly increases the likelihood of successful compromise in environments where default credentials remain unchanged or administrative passwords are weak.
Mitigation strategies must prioritize immediate remediation through firmware updates provided by TOTOLINK that address this specific input validation flaw. If an update is not immediately available, network administrators should restrict access to the router's web management interface using firewall rules, ensuring it is only reachable from trusted internal IP addresses rather than exposing it directly to the internet. Additionally, enforcing strong, unique administrative passwords and disabling remote administration features when not strictly necessary can reduce the attack surface. From a defensive monitoring perspective, security teams should look for anomalous HTTP requests containing shell metacharacters in parameters related to CGI scripts or VPN configurations, which aligns with ATT&CK technique T1059: Command and Scripting Interpreter usage by adversaries during initial access or lateral movement phases.