CVE-2026-51716 in TOTOLINK
Summary
by MITRE • 08/31/2026
Incorrect access control in the delPortForwardRules function of TOTOLINK T6 4.1.5cu.748_B20211015 allows unauthenticated attackers to delete port-forwarding rules 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 TOTOLINK T6 router, specifically within firmware version 4.1.5cu.748_B20211015, represents a critical failure in access control mechanisms governing network configuration functions. The flaw resides in the delPortForwardRules function, which is responsible for removing port-forwarding rules from the device's NAT table. This component fails to enforce proper authentication or authorization checks before executing state-changing operations on the router’s firewall and routing configurations. Consequently, any unauthenticated attacker who can reach the administrative interface of the router over the network can exploit this weakness by sending a specifically crafted POST request to the /cgi-bin/cstecgi.cgi endpoint. This lack of validation allows external actors to bypass security controls that should restrict such sensitive operations to authenticated administrators only.
From a technical perspective, the exploitation vector relies on the direct invocation of an administrative CGI script without requiring valid session tokens or credentials. In typical secure implementations, functions that modify critical system settings like port forwarding must verify user privileges before proceeding with execution. Here, the absence of these checks means that the router processes the deletion request as if it originated from a legitimate administrator. This type of flaw is commonly categorized under CWE-269, which denotes Improper Privilege Assignment, and aligns with ATT&CK technique T1078, Valid Accounts, although in this case, no valid account is even required due to the complete lack of authentication enforcement for specific high-risk functions. The attacker can manipulate network traffic rules at will, effectively altering how inbound connections are directed within the local network topology.
The operational impact of this vulnerability is significant and multifaceted. By deleting port-forwarding rules, an attacker can disrupt services hosted on devices behind the router that rely on these mappings for external accessibility, leading to denial of service conditions for those specific applications. More critically, if the attacker has prior knowledge or control over other parts of the network, they could delete existing security boundaries while simultaneously creating new, malicious port-forwarding rules to expose internal systems directly to the internet without proper filtering. This capability undermines the fundamental purpose of a router as a perimeter defense device, potentially exposing sensitive internal assets such as IoT devices, servers, or workstations to direct attack from untrusted networks. The ability to arbitrarily modify firewall and NAT configurations effectively neutralizes one layer of network segmentation and protection.
Mitigation strategies for this vulnerability primarily involve immediate firmware updates provided by the vendor that patch the access control logic within the delPortForwardRules function. Until such a patch is available, administrators should restrict physical or remote access to the router’s management interface using strong authentication mechanisms if supported in earlier versions, although given the nature of the flaw, reliance on network-level restrictions like IP whitelisting for administrative ports may offer temporary relief but does not address the root cause. Network segmentation and monitoring can also help detect anomalous POST requests targeting CGI endpoints associated with configuration changes. Ultimately, enforcing strict authentication requirements for all administrative functions is essential to prevent unauthorized modification of critical network settings.