CVE-2026-51679 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setPasswordCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to change the administrator account via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in TOTOLINK T6 router firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms within the device's web management interface. Specifically, the flaw resides in the setPasswordCfg function, which is responsible for modifying administrative credentials. This component fails to enforce proper authentication checks before processing requests that alter sensitive configuration parameters. As a result, any actor with network-level connectivity to the router can exploit this weakness without needing valid login credentials or session tokens. The attack vector involves sending a specifically crafted HTTP POST request to the endpoint /cgi-bin/cstecgi.cgi. This path is commonly used by embedded devices for handling CGI scripts that manage device settings, and in this instance, it serves as the entry point for unauthorized privilege escalation.
From a technical perspective, the root cause of this vulnerability lies in the lack of input validation and authentication verification within the server-side logic governing administrative changes. When an unauthenticated user submits data to the setPasswordCfg function via the cstecgi.cgi script, the system processes the request as if it originated from an authenticated administrator session. This behavior violates fundamental security principles regarding separation of duties and privilege management. The absence of a valid authentication token or session identifier in the request processing pipeline allows attackers to bypass standard login procedures entirely. By manipulating specific fields within the POST payload, such as username and password hashes or plaintext credentials depending on implementation details, an attacker can overwrite existing administrative accounts with new ones under their control. This effectively grants full administrative access to the device without prior authorization.
The operational impact of this vulnerability is severe, as it leads directly to complete compromise of the affected network infrastructure. Once an attacker successfully changes the administrator password, they gain unrestricted access to all configuration options available through the web interface. This includes the ability to modify firewall rules, open ports for remote management protocols such as SSH or Telnet, alter DNS settings to facilitate phishing or man-in-the-middle attacks, and potentially install malicious firmware updates if the device allows unsigned uploads. Furthermore, because routers often serve as gateways between internal local networks and external internet connections, compromising this single device can expose all connected devices within the LAN to further exploitation. Attackers may use the compromised router to intercept traffic, inject malware into unencrypted HTTP streams, or pivot deeper into corporate or home network environments where sensitive data resides.
This vulnerability aligns with Common Weakness Enumeration (CWE) category CWE-284, which describes Improper Access Control, and more specifically reflects aspects of CWE-306 regarding the Missing Authentication for Critical Function. In terms of offensive security frameworks like MITRE ATT&CK, this flaw facilitates initial access through exploitation of application-level vulnerabilities and enables privilege escalation by allowing an unauthenticated user to assume administrative roles. The attack technique corresponds to T1190 Exploit Public-Facing Application, as it leverages a publicly accessible or network-accessible service to gain foothold in the system.
Mitigation strategies for this vulnerability primarily involve immediate firmware updates provided by TOTOLINK that patch the authentication logic within the setPasswordCfg function. Until an official patch is applied, administrators should restrict access to the router's management interface using firewall rules, ensuring it is only reachable from trusted internal IP addresses rather than exposed directly to untrusted networks or the internet. Additionally, disabling remote management features if they are not strictly necessary reduces the attack surface significantly. Network segmentation can also help limit lateral movement in case a device is compromised, isolating critical assets from potentially vulnerable IoT devices. Regular auditing of configuration changes and monitoring for unusual administrative logins can aid in early detection of exploitation attempts.