CVE-2026-51676 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setAccessDeviceCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to alter access-device policies 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 setAccessDeviceCfg function within TOTOLINK T6 firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms, specifically classified under CWE-284 Improper Access Control. This flaw allows unauthenticated remote attackers to manipulate device configuration settings without providing valid credentials or session tokens. The core technical issue lies in the insufficient validation of authentication states before processing administrative commands sent through the web interface. By targeting the /cgi-bin/cstecgi.cgi endpoint, which serves as a common gateway for executing CGI scripts on embedded Linux-based routers and network devices, an attacker can bypass standard security checks that are typically enforced by the application logic or session management subsystems.
The operational impact of this vulnerability is severe, as it grants unauthorized users the ability to alter access-device policies remotely. These policies often dictate firewall rules, port forwarding configurations, DNS settings, and other critical network parameters that govern how traffic flows through the device. An attacker exploiting this flaw could redirect internet-bound traffic from legitimate users to malicious servers for interception or data theft, open specific ports to expose internal services to the public internet, or disable security features such as intrusion detection systems or parental controls. This effectively compromises the integrity and confidentiality of the entire network segment protected by the router, turning a trusted gateway into an instrument for further attacks against connected devices.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1059 Command and Scripting Interpreter, as it involves sending crafted HTTP POST requests to execute administrative functions via CGI scripts. It also relates to T1484 Domain Policy Modification if the access policies involve domain-level restrictions or DNS configurations. The exploitation requires no prior authentication, which significantly lowers the barrier for entry, making this vulnerability susceptible to automated scanning and widespread propagation by malicious actors seeking to compromise large numbers of IoT devices for botnet recruitment or as pivot points in larger network intrusions.
Mitigation strategies must focus on immediate patching if a vendor update is available that addresses the access control logic within the setAccessDeviceCfg function. In cases where patches are not immediately accessible, administrators should restrict external access to the management interface by configuring firewalls to allow only trusted IP addresses or internal subnets to reach the /cgi-bin/cstecgi.cgi endpoint. Additionally, enabling strong administrative passwords and disabling remote administration features when not strictly necessary can reduce the attack surface. Network segmentation is also recommended to limit the blast radius in case of compromise, ensuring that critical assets are isolated from potentially vulnerable edge devices. Continuous monitoring for unusual outbound traffic patterns or configuration changes can aid in early detection of exploitation attempts.