CVE-2026-51619 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getOnlineClient function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain online client information 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 the getOnlineClient function of TOTOLINK T6 router 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 retrieve sensitive network topology information by interacting with the device's web management interface. The attack vector involves sending a specially crafted HTTP POST request to the endpoint /cgi-bin/cstecgi.cgi, which serves as the gateway for various administrative and status retrieval functions within the router’s firmware. Because the function does not adequately verify the authentication state of the requester before processing the query, it exposes internal network data that should be restricted to authorized administrators only.
From a technical perspective, the getOnlineClient function is designed to return details about devices currently connected to the local area network, such as IP addresses, MAC addresses, and potentially hostnames or connection durations. In a properly secured implementation, this endpoint would require valid session tokens or administrative credentials before executing the query. However, due to the misconfiguration or coding error in this specific firmware version, the access control check is either bypassed entirely or not implemented for this particular CGI script. This allows an attacker who has network reachability to the router’s management interface—whether through a local wired connection or potentially over the internet if remote administration is enabled—to extract this information without any form of authentication. The simplicity of the attack, requiring only a crafted POST request, highlights a fundamental lack of input validation and privilege verification in the web server logic handling these requests.
The operational impact of this vulnerability extends beyond simple data leakage; it serves as a significant reconnaissance tool for further exploitation. By obtaining a list of online clients, an attacker can map the internal network structure, identifying active devices such as computers, smartphones, IoT sensors, or other routers. This information is crucial for planning subsequent attacks, such as targeted phishing against specific users, exploiting vulnerabilities in identified client operating systems, or launching denial-of-service attacks against critical infrastructure components within the LAN. Furthermore, knowledge of MAC addresses and IP configurations can facilitate ARP spoofing or man-in-the-middle attacks to intercept traffic between clients and the gateway. The exposure of this data undermines the confidentiality integrity of the network environment managed by the router.
This vulnerability aligns with several entries in the MITRE ATT&CK framework, particularly T1046: Network Service Discovery, where adversaries probe for services that can be used to discover devices on a local or remote network. It also relates to T1539: Steal Web Session Cookie if session management is compromised later, although the primary issue here is direct data exfiltration without authentication. The flaw exemplifies common pitfalls in embedded device development where convenience often overrides security, leading to endpoints that are accessible by default with insufficient restrictions.
Mitigation for this vulnerability requires immediate action from both users and manufacturers. For end-users, the most effective step is to update the router firmware to a patched version released after October 15, 2021, which addresses the access control logic in the cstecgi.cgi script. If an updated firmware is not available or cannot be applied immediately, administrators should disable remote management features entirely and ensure that the web interface is only accessible from trusted internal networks rather than exposed to the public internet. Additionally, changing default administrative passwords and implementing strong network segmentation can limit the blast radius if an attacker gains initial access. For developers and vendors, this incident underscores the necessity of enforcing strict authentication checks on all CGI endpoints, particularly those returning sensitive operational data, and conducting regular security audits focused on improper access control flaws in embedded web interfaces.