CVE-2026-51717 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setOpModeCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to change the device operating mode 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 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 setOpModeCfg function, which is responsible for configuring the operational mode of the router or wireless access point. This component typically handles sensitive configuration changes that determine how the device operates, such as switching between router, bridge, repeater, or other network roles. The core issue arises because this administrative function does not enforce proper authentication checks before processing incoming requests. Consequently, any entity capable of reaching the web server interface can invoke this functionality without providing valid credentials, effectively bypassing the intended security boundaries designed to protect device configuration integrity.
From a technical perspective, an unauthenticated attacker can exploit this flaw by sending a specifically crafted HTTP POST request to the endpoint /cgi-bin/cstecgi.cgi. This CGI script acts as the backend processor for various administrative tasks on TOTOLINK devices. By manipulating the parameters within the POST body, typically involving JSON or form-encoded data that specifies the desired operating mode, an attacker can force the device into a state defined by their input. Since there is no session validation or token verification associated with this specific endpoint in the affected firmware version, the server accepts and executes these commands as if they originated from an authorized administrator. This lack of authorization logic allows for remote configuration changes without any form of user interaction or credential disclosure, making it a straightforward exploitation vector for individuals with network access to the device's management interface.
The operational impact of this vulnerability is significant, particularly in environments where devices are exposed to untrusted networks or have open administrative ports accessible from the internet. An attacker who successfully exploits this flaw can alter the fundamental behavior of the networking equipment. For instance, changing the operating mode might disable security features such as firewall rules, Wi-Fi encryption, or access control lists that are tied to specific modes. Furthermore, reconfiguring the device could redirect traffic through malicious infrastructure if the new mode involves bridging or routing changes that an attacker controls. This capability undermines the confidentiality and integrity of network communications managed by the device. In severe cases, it may facilitate further attacks such as man-in-the-middle scenarios, DNS spoofing, or complete denial of service by disrupting normal connectivity patterns. The ability to change operating modes remotely also complicates incident response efforts, as the attacker can potentially mask their presence or alter logging behaviors depending on the selected mode.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically highlighting failures where authorization checks are missing or ineffective for critical functions. It is also relevant to MITRE ATT&CK technique T1078, Valid Accounts, as it allows an attacker to achieve administrative privileges without valid credentials by exploiting the system's trust in unauthenticated requests. To mitigate this risk, users of TOTOLINK T6 devices running version 4.1.5cu.748_B20211015 should immediately update their firmware to a patched version where access control checks have been implemented for the setOpModeCfg function and related administrative endpoints. If an immediate patch is unavailable, network administrators should restrict access to the device's web management interface by placing it behind a firewall that only allows connections from trusted IP addresses or internal subnets. Additionally, disabling remote administration features if they are not strictly necessary can reduce the attack surface exposed to potential attackers on external networks. Regularly auditing configuration changes and monitoring for unusual traffic patterns directed at CGI endpoints can also aid in early detection of exploitation attempts.