CVE-2026-51733 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the FirmwareUpgrade function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to remove Wi-Fi schedule entries 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 the TOTOLINK T6 router, specifically within firmware version 4.1.5cu.748_B20211015, represents a critical failure in access control mechanisms governing administrative functions. The core issue resides in the FirmwareUpgrade function and its associated CGI endpoint located at /cgi-bin/cstecgi.cgi. This component is designed to handle configuration changes for the device, including Wi-Fi scheduling parameters which dictate when wireless networks are active or inactive based on predefined time windows. In a properly secured system, any operation that modifies critical network settings must require authentication from an authorized administrator with appropriate privileges. However, in this instance, the implementation fails to enforce these security boundaries effectively.
Unauthenticated attackers can exploit this flaw by sending crafted POST requests directly to the specified CGI endpoint without providing valid credentials or session tokens. This lack of authorization checks allows external actors to manipulate the router's configuration remotely over the local network or potentially via port forwarding if exposed to the internet. The specific impact involves the ability to remove Wi-Fi schedule entries, which are essential for managing wireless access policies such as parental controls, guest network isolation schedules, or energy-saving modes that automatically disable radios during off-hours. By deleting these scheduled tasks, an attacker can disrupt normal operational workflows and leave the wireless interface in a default state where it may remain perpetually active regardless of intended restrictions.
From a technical perspective, this vulnerability aligns with CWE-284 Improper Access Control, as the application does not properly restrict access to resources based on user identity or privileges. The attack vector is classified under ATT&CK technique T1505.003 Server Software Component: Web Shell, although in this context it manifests more directly as unauthorized configuration modification rather than persistent code execution. However, the ability to alter system configurations via unauthenticated web requests also touches upon CWE-648 Incorrect Registration of Ownership and Control of Resource, where the resource (Wi-Fi schedule) is not correctly bound to authenticated administrative sessions. The exploitation requires no special privileges beyond network connectivity to the router's management interface, making it a low-complexity attack that can be automated easily using standard HTTP client tools or scripts.
The operational impact of this vulnerability extends beyond mere inconvenience. Wi-Fi schedules are often used as part of broader security strategies, such as limiting exposure time for IoT devices or enforcing quiet hours in residential environments. Removing these entries effectively neutralizes these controls, potentially exposing connected devices to increased risk during periods when they should be isolated or powered down. Furthermore, the ability to modify configuration settings without authentication undermines the integrity of the device's management plane. If an attacker can delete schedule entries, it is highly probable that other unprotected endpoints within the same CGI handler could also be manipulated to change SSID names, passwords, or firewall rules, leading to a complete compromise of network security posture.
Mitigation strategies for this vulnerability primarily involve updating the firmware to a patched version released by TOTOLINK where proper authentication checks have been implemented in the FirmwareUpgrade function and related CGI handlers. Until an official patch is available, administrators should restrict access to the router's management interface through firewall rules that limit IP addresses allowed to reach port 80 or 443 exclusively to trusted internal subnets. Additionally, disabling remote administration features if they are not strictly necessary reduces the attack surface significantly. Network segmentation can also help contain potential lateral movement by isolating IoT devices and other critical infrastructure from general user networks where such exploitation might originate. Regular auditing of configuration changes and monitoring for unauthorized access attempts via web server logs provide additional layers of defense against this type of misconfiguration-based exploit.