CVE-2026-51718 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the delStaticDhcpRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to remove static DHCP reservations via sending a crafted POST request to /cgi-bin/cstecgi.cgi.
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Analysis
by VulDB Data Team • 08/31/2026
The vulnerability identified in the delStaticDhcpRules function within TOTOLINK T6 firmware version 4.1.5cu.748_B20211015 represents a critical failure in access control mechanisms, specifically categorized under CWE-284 Improper Access Control. This flaw permits unauthenticated actors to execute administrative functions that should be restricted to authorized users with valid credentials. The core technical issue lies in the absence of proper authentication checks or session validation within the CGI script responsible for managing static DHCP reservations. By sending a specially crafted POST request to the endpoint /cgi-bin/cstecgi.cgi, an attacker can bypass security controls and directly invoke this function without providing any form of identification or authorization token. This lack of enforcement allows external entities to interact with sensitive configuration parameters as if they were legitimate administrators, undermining the integrity of the device's network management capabilities.
The operational impact of this vulnerability is significant for both residential and small business networks relying on TOTOLINK routers for stable IP address assignment. Static DHCP reservations are essential for ensuring that specific devices always receive the same local IP address, which is crucial for services such as port forwarding, remote access servers, or network monitoring tools. When an attacker successfully exploits this flaw, they can remove these static assignments at will. This action forces affected devices to request new addresses via dynamic host configuration protocol processes, potentially leading to service disruptions if critical systems lose their expected IP bindings. Furthermore, the ability to manipulate DHCP configurations without authentication opens the door for further network manipulation attacks, such as DNS spoofing or man-in-the-middle scenarios by assigning malicious gateway information through other compromised settings, although this specific CVE focuses on the removal of reservations.
From a threat intelligence perspective, this vulnerability aligns with ATT&CK technique T1078 Valid Accounts if an attacker were to use stolen credentials, but in its current unauthenticated state, it falls under privilege escalation or unauthorized configuration modification patterns often seen in IoT device exploitation chains. The attack vector is remote and requires no user interaction beyond sending a network packet, making it highly scalable for automated scanning tools targeting vulnerable router models across the internet. Attackers can leverage this to destabilize local networks, disrupt connectivity for specific hosts, or prepare the ground for more complex intrusions by altering network topology settings.
Mitigation strategies must prioritize immediate patching if an updated firmware version is available from TOTOLINK that addresses this access control deficiency. In cases where updates are not immediately deployable, administrators should restrict physical and remote access to the router's management interface using firewall rules or VLAN segmentation to limit exposure to untrusted networks. Additionally, changing default administrative passwords and disabling remote administration features can reduce the attack surface. Network monitoring solutions should be configured to detect anomalous POST requests directed at CGI endpoints with unusual parameters indicative of DHCP manipulation attempts. Long-term remediation involves implementing strict input validation and enforcing authentication checks on all administrative functions within embedded web interfaces to prevent unauthorized state changes.