CVE-2026-51615 in TOTOLINK
Summary
by MITRE • 08/28/2026
Incorrect access control in the getLanCfg function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to obtain LAN addressing and DHCP configuration 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 TOTOLINK T6 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 getLanCfg function, which is designed to retrieve Local Area Network configuration details such as IP addressing schemes and Dynamic Host Configuration Protocol settings. Under normal operational conditions, this functionality should be restricted to authenticated administrators who have successfully logged into the router’s administrative panel. However, due to insufficient validation of user privileges before processing requests, an unauthenticated attacker can bypass these security controls entirely. This misconfiguration allows external actors with network access to interact directly with sensitive configuration endpoints without providing valid credentials or session tokens.
The technical mechanism exploited involves sending a specifically crafted HTTP POST request to the /cgi-bin/cstecgi.cgi endpoint. By targeting this specific gateway script, which serves as an interface between the web server and backend system commands, attackers can trigger the execution of the getLanCfg function without authentication checks being enforced by the application logic. This lack of authorization enforcement means that any entity capable reaching the router over the network layer can invoke this method. The resulting response contains detailed information regarding the LAN subnet mask, default gateway IP address, and DHCP server range configurations. Such data is fundamental to understanding the internal network topology and operational parameters of the target device.
The operational impact of this vulnerability extends beyond simple information disclosure. While obtaining static configuration details like IP addresses may seem limited in isolation, it serves as a critical reconnaissance step for further exploitation. Knowledge of the LAN subnet structure allows attackers to map out the local network environment more accurately than through passive scanning alone. Furthermore, exposure of DHCP configuration parameters can facilitate man-in-the-middle attacks or rogue access point deployments if combined with other vulnerabilities. In many IoT and networking devices, such information is often correlated with default credentials or known API endpoints for remote management protocols like TR-069 or UPnP, thereby increasing the attack surface significantly. The ability to extract this data without authentication lowers the barrier to entry for automated scanning tools and script-kiddie attacks, making widespread exploitation highly probable in environments where these routers are deployed.
From a classification perspective, this vulnerability aligns with CWE-284, which describes Improper Access Control, specifically falling under scenarios where access control decisions are not properly enforced before granting access to resources. Additionally, the behavior corresponds to ATT&CK technique T1078, Valid Accounts, although in this case it is more accurately described as unauthorized access due to missing authentication requirements rather than stolen credentials. The exploitation vector falls under Remote Code Execution or Information Disclosure depending on subsequent actions taken by the attacker, but primarily constitutes an Unauthorized Access to Sensitive Information scenario within the MITRE ATT&CK framework for network devices.
Mitigation strategies must focus on enforcing strict authorization checks at the application layer before any configuration retrieval functions are executed. Developers should implement role-based access control that verifies user session validity and administrative privileges prior to processing requests directed at sensitive CGI endpoints like cstecgi.cgi. Input validation alone is insufficient; explicit authentication middleware or token verification mechanisms must be integrated into the request handling pipeline for all management interfaces. For immediate remediation, users of affected firmware versions should update their devices to a patched release where this access control flaw has been resolved by the vendor. In cases where updates are not immediately available, network segmentation can help limit exposure by restricting direct internet-facing access to the router’s administrative interface and placing it behind additional firewall rules that require strong authentication or IP whitelisting for management traffic.