CVE-2026-19815 in A800R
Summary
by MITRE • 08/14/2026
A flaw has been found in TOTOLINK A800R 4.1.2cu.5137_B20200730. Affected by this vulnerability is the function setParentalRules of the file /cgi-bin/cstecgi.cgi of the component firewall.so. Executing a manipulation of the argument urlKeyword can lead to stack-based buffer overflow. It is possible to launch the attack remotely. The exploit has been published and may be used.
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Analysis
by VulDB Data Team • 08/14/2026
The vulnerability identified in TOTOLINK A800R router firmware version 4.1.2cu.5137_B20200730 represents a critical stack-based buffer overflow flaw within the firewall.so component of the device's web interface. This issue manifests through the setParentalRules function located in the /cgi-bin/cstecgi.cgi file, which processes user input without adequate bounds checking mechanisms. The specific attack vector involves manipulation of the urlKeyword argument parameter, which when improperly handled by the vulnerable software component creates an exploitable condition that can be triggered remotely.
The technical implementation of this vulnerability stems from inadequate input validation within the firewall.so module where the urlKeyword parameter is processed during parental control rule configuration. When an attacker crafts malicious input for this parameter, the system fails to properly validate or limit the length of the supplied data before copying it into a fixed-size stack buffer. This classic buffer overflow condition allows an attacker to overwrite adjacent memory locations including return addresses and function pointers, potentially enabling arbitrary code execution with elevated privileges. The vulnerability is particularly concerning as it operates through the web-based administration interface, eliminating the need for physical access or local network presence.
From an operational perspective, this remote exploit capability presents significant security implications for users of the affected TOTOLINK A800R devices. The attack can be initiated from any location with network connectivity to the router's administrative interface, making it accessible to threat actors worldwide without requiring specialized physical access. Successful exploitation could result in complete system compromise, allowing attackers to modify firewall rules, gain persistent access, or even install malicious firmware. The fact that a public exploit exists further amplifies the risk level, as it removes the barrier to entry for potential attackers who may not possess advanced exploitation skills. Network administrators face the challenge of protecting devices that are likely to remain unpatched due to the device's age and limited support lifecycle.
The vulnerability aligns with CWE-121 Stack-based Buffer Overflow, which is categorized under the weakness type that directly enables arbitrary code execution through memory corruption. From an ATT&CK framework perspective, this represents a technique that could be leveraged for privilege escalation and persistence within targeted networks. The attack surface is particularly dangerous in enterprise environments where these devices may be deployed without proper network segmentation or monitoring. Organizations should implement immediate mitigations including disabling unnecessary web administration services, applying network-level restrictions such as firewall rules limiting access to the affected interface, and conducting comprehensive inventory audits to identify all affected devices. Additionally, the device firmware should be updated to a patched version if available, or replaced with a more secure alternative that receives regular security updates and support from the manufacturer.