CVE-2026-51649 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getDiagnosisCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain diagnostic configuration and ping log contents 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 getDiagnosisCfg function, which is exposed through the Common Gateway Interface script located at /cgi-bin/cstecgi.cgi. This architectural oversight allows unauthenticated actors to interact with sensitive diagnostic endpoints that should strictly require administrative privileges or valid session tokens for access. By sending a crafted POST request to this specific endpoint, an attacker can bypass authentication checks entirely, demonstrating a fundamental misconfiguration in how the router validates user permissions before executing privileged operations.
From a technical perspective, the exploitation of this vulnerability relies on the lack of proper input validation and authorization enforcement within the CGI script handling diagnostic requests. The getDiagnosisCfg function is designed to retrieve configuration data related to network diagnostics, but it fails to verify whether the requesting entity possesses the necessary credentials. This allows remote attackers who are not logged in as administrators to extract sensitive information directly from the device's memory or storage without any prior authentication step. The ability to send a POST request suggests that the vulnerability may also be exploitable via automated tools, facilitating mass exploitation across networks running this specific firmware version.
The operational impact of this vulnerability is significant due to the nature of the data exposed. An attacker can obtain diagnostic configuration details and ping log contents, which provide deep insights into the network topology and recent connectivity attempts. Diagnostic configurations may reveal internal IP addresses, gateway settings, DNS servers, and other structural elements of the local area network that are not intended for public or unauthenticated view. Furthermore, access to ping logs allows an attacker to map active hosts on the network by analyzing timestamps and target IPs recorded in these logs. This information is highly valuable for reconnaissance purposes, enabling further targeted attacks such as man-in-the-middle attempts, session hijacking, or lateral movement within the compromised network segment.
This vulnerability aligns with CWE-284, which describes Improper Access Control, specifically where a system fails to enforce proper authorization checks before allowing access to sensitive resources. In terms of offensive security frameworks, this behavior corresponds to ATT&CK technique T1078, Valid Accounts, although in this case the attacker does not need valid accounts at all due to the authentication bypass. It also relates to T1592, Gather Victim Host Information, as the extracted diagnostic data aids in profiling the target environment. The exposure of internal network details through ping logs further supports reconnaissance activities classified under information gathering techniques that precede more destructive exploits like privilege escalation or data exfiltration.
Mitigation strategies for this vulnerability primarily involve immediate firmware updates provided by TOTOLINK to patch the access control logic within the getDiagnosisCfg function. Administrators should verify their router's current version and apply any available security patches that address authentication bypass issues in CGI scripts. In cases where updating is not immediately feasible, network segmentation can help limit exposure; placing management interfaces on isolated VLANs restricts unauthenticated access from general user networks. Additionally, disabling remote management features if they are not strictly necessary reduces the attack surface by preventing external actors from even reaching the vulnerable endpoint. Regular auditing of router configurations and monitoring for unusual POST requests to CGI scripts can also aid in early detection of exploitation attempts before significant data loss occurs.