CVE-2026-51645 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getPasswordCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain the administrative username via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/28/2026
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 getPasswordCfg function, which is invoked when handling POST requests directed to the /cgi-bin/cstecgi.cgi endpoint. This architectural weakness allows unauthenticated attackers to bypass standard authentication protocols and extract sensitive administrative credentials from the system. The core issue stems from a lack of proper authorization checks before processing configuration retrieval commands that are intended for privileged users only, thereby exposing internal state data to external actors without any form of credential validation or session verification.
From a technical perspective, this vulnerability is classified under CWE-284, which denotes Improper Access Control, and aligns with the ATT&CK technique T1078, Valid Accounts, as it enables an attacker to leverage existing administrative privileges by extracting them rather than creating new ones. The exploitation vector involves sending a specifically crafted HTTP POST request to the designated CGI script. Because the server fails to verify whether the requester possesses valid administrator rights or an active authenticated session prior to executing the getPasswordCfg function, the system proceeds to serialize and return configuration data that includes plaintext administrative usernames. This behavior indicates a fundamental misunderstanding of security boundaries within the embedded web server implementation, where sensitive management endpoints are treated with insufficient isolation from public-facing interfaces.
The operational impact of this vulnerability is severe for network administrators relying on TOTOLINK T6 devices in both home and small business environments. By obtaining the administrative username through an unauthenticated request, attackers gain a crucial piece of intelligence required to launch targeted brute-force attacks or credential stuffing campaigns against the device's login page. While the password itself may not be immediately exposed by this specific flaw, knowing the exact username significantly reduces the attack surface for subsequent exploitation attempts. This can lead to full compromise of the router, allowing an attacker to intercept network traffic, redirect DNS queries, install malicious firmware, or use the compromised device as a pivot point for further intrusion into the local area network.
Mitigation strategies must prioritize immediate patching and configuration hardening. Users should update their TOTOLINK T6 routers to the latest available firmware version released by the vendor, which likely includes fixes for this access control bypass. In cases where updating is not immediately feasible, administrators can implement network-level controls such as firewall rules that restrict access to /cgi-bin/cstecgi.cgi exclusively from trusted internal IP addresses or management VLANs. Additionally, changing default administrative usernames and enforcing strong password policies can mitigate the risk associated with username enumeration by increasing the complexity of subsequent brute-force attempts. Regular security audits and monitoring for unusual POST traffic patterns on the management interface are also recommended to detect potential exploitation activities early.