CVE-2026-51742 in TOTOLINK
Summary
by MITRE • 09/01/2026
Incorrect access control in the discoverWan function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to trigger WAN discovery logic via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 09/01/2026
The vulnerability identified in the discoverWan 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 interact with internal network discovery logic without providing valid credentials or session tokens. The attack vector involves sending a specially crafted HTTP POST request directly to the /cgi-bin/cstecgi.cgi endpoint, which serves as the primary interface for executing various router management functions. By bypassing authentication checks that should be enforced before processing sensitive configuration queries, an attacker can exploit this misconfiguration to extract detailed information about the device's external network environment.
From a technical perspective, the discoverWan function is designed to query and return details regarding the Wide Area Network connection status, including IP addresses assigned by the ISP, gateway configurations, and potentially DNS server settings. When access control is improperly implemented or entirely absent for this specific CGI script invocation, any entity with network connectivity to the router can trigger this logic. The crafted POST request likely manipulates parameters within the HTTP body to force the firmware to execute the discovery routine and return its output directly in the response payload. This behavior indicates a lack of input validation combined with insufficient authorization checks at the application layer, allowing external actors to read sensitive network topology data that should be restricted to authenticated administrators only.
The operational impact of this vulnerability is significant for both individual users and enterprise environments relying on these devices for secure connectivity. The primary consequence is information disclosure, where attackers can gather critical intelligence about the internal network structure behind the NAT gateway. Knowledge of public IP addresses, subnet masks, and DNS configurations aids in further reconnaissance activities, such as mapping out adjacent networks or identifying potential targets within a broader infrastructure. Furthermore, if the discovery logic interacts with other system components to update routing tables or trigger reconnections, an attacker could potentially induce denial-of-service conditions by forcing repeated WAN resets or exhausting router resources through rapid-fire requests. This undermines the integrity and availability of the network edge device.
This vulnerability aligns with MITRE ATT&CK technique T1046 Network Service Discovery, where adversaries probe networks to identify active services and systems for subsequent exploitation. The ability to access this data without authentication also relates to CWE-89 Improper Neutralization of Special Elements used in an SQL Command or general input handling flaws if the parameters are not sanitized before processing, although the core issue remains authorization failure. To mitigate this risk, users should immediately update their TOTOLINK T6 firmware to a version where access control for CGI endpoints is strictly enforced and requires valid administrative authentication tokens. Network administrators should also consider placing these devices behind additional security layers such as firewalls that restrict direct HTTP/HTTPS access from untrusted networks or implement network segmentation to limit exposure of management interfaces. Regular vulnerability scanning and monitoring for unusual POST traffic patterns targeting /cgi-bin/cstecgi.cgi can help detect exploitation attempts in real-time before significant damage occurs.