CVE-2026-51690 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the setWanCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to alter upstream provisioning and connectivity 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 network configuration parameters. This flaw resides within the setWanCfg function, which is responsible for configuring Wide Area Network settings such as PPPoE credentials, static IP addresses, and gateway information. The core technical issue stems from an insufficient validation of authentication tokens or session states when processing HTTP POST requests directed at the /cgi-bin/cstecgi.cgi endpoint. In a properly secured system, any attempt to modify critical network infrastructure settings should require valid administrative credentials and a verified active session. However, in this instance, the application logic fails to enforce these prerequisites, allowing unauthenticated actors to interact with sensitive configuration endpoints directly over the network interface.
From an operational perspective, this lack of authentication allows remote attackers who have network access to the router's management plane to alter upstream provisioning parameters without authorization. By sending a crafted POST request containing maliciously formatted data, an attacker can overwrite existing WAN settings, effectively hijacking the device's internet connectivity configuration. This capability enables several detrimental outcomes including redirecting traffic through unauthorized gateways for man-in-the-middle attacks, disabling internet access entirely to cause denial of service, or configuring DNS servers under the attacker's control to facilitate phishing campaigns and domain spoofing. The impact is severe because WAN settings are fundamental to the router's primary function of providing network connectivity; compromising them undermines both confidentiality and availability guarantees for all devices connected behind this gateway.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically highlighting failures in enforcing authorization policies on critical functions. Furthermore, it maps directly to MITRE ATT&CK technique T1078, Valid Accounts, although in this case the exploitation does not require valid credentials but rather exploits the absence of required authentication checks entirely. The attack vector is classified as Network-based with Low Complexity due to the straightforward nature of crafting HTTP POST requests using standard web tools or scripts. Attackers can exploit this remotely if they are on the same local network segment, and potentially over the internet if UPnP or port forwarding rules expose the management interface externally without additional security layers like CAPTCHA or rate limiting that might inadvertently mitigate such automated attacks in some implementations.
Mitigation strategies must prioritize immediate patching to a firmware version where access control checks have been properly implemented within the setWanCfg function and related CGI handlers. Until patches are available, network administrators should restrict physical and logical access to the router's management interface by disabling remote administration features if not strictly necessary. Implementing strict firewall rules that limit HTTP/HTTPS traffic on administrative ports to trusted IP addresses only can significantly reduce the attack surface. Additionally, enabling WPA3 encryption for wireless networks and changing default SSIDs helps prevent unauthorized devices from joining the local network where they could attempt exploitation of this vulnerability. Regular audits of connected devices and monitoring for unusual configuration changes via router logs are also recommended practices to detect potential compromise attempts early.