CVE-2026-4535 is a stack-based buffer overflow vulnerability identified in the Tenda FH451 router firmware version 1.0.0.9. The flaw resides in the WrlclientSet function, specifically in the handling of the GO argument within the /goform/WrlclientSet endpoint. Improper validation or bounds checking of this argument allows an attacker to overflow the stack buffer, potentially overwriting critical control data such as return addresses. This can lead to arbitrary code execution with elevated privileges on the device. The vulnerability is remotely exploitable over the network without requiring authentication or user interaction, making it highly dangerous. The CVSS 4.0 score of 8.7 reflects its high impact on confidentiality, integrity, and availability, combined with low attack complexity and no prerequisites. Although no active exploits have been reported in the wild, the public disclosure of the exploit code increases the likelihood of future attacks. The affected product, Tenda FH451, is a consumer and small office/home office (SOHO) router, commonly deployed in various global markets. The vulnerability could be leveraged by attackers to gain persistent control over the device, intercept or manipulate network traffic, or launch further attacks within the local network or against external targets. Due to the lack of an official patch at the time of disclosure, mitigation relies on network-level controls and configuration changes.

The exploitation of CVE-2026-4535 can have severe consequences for organizations and individuals using the Tenda FH451 router. Successful attacks may lead to full compromise of the router, allowing attackers to execute arbitrary code with elevated privileges. This can result in interception and manipulation of network traffic, unauthorized access to internal networks, disruption of internet connectivity, and use of the compromised device as a foothold for lateral movement or launching attacks against other targets. The confidentiality of sensitive data traversing the network can be breached, integrity of communications compromised, and availability of network services disrupted. For organizations, this can mean data breaches, operational downtime, and reputational damage. The remote and unauthenticated nature of the exploit increases the attack surface and risk, especially for devices exposed to the internet or poorly segmented networks. The lack of known exploits in the wild currently limits immediate widespread impact, but the public availability of exploit details raises the risk of rapid weaponization.

1. Apply firmware updates from Tenda as soon as they become available to patch the vulnerability. Monitor vendor communications for official patches or advisories. 2. If patches are not yet available, disable remote management interfaces on the Tenda FH451 router to prevent external exploitation. 3. Implement network segmentation to isolate vulnerable devices from critical internal networks and sensitive data. 4. Use firewall rules to restrict access to the /goform/WrlclientSet endpoint and block suspicious traffic targeting this URI. 5. Monitor network traffic and device logs for unusual activity or repeated requests to the vulnerable endpoint, which may indicate exploitation attempts. 6. Consider replacing affected devices with models from vendors with more robust security track records if patching is delayed. 7. Educate network administrators about the vulnerability and ensure incident response plans include steps for handling potential exploitation. 8. Employ intrusion detection/prevention systems (IDS/IPS) with updated signatures to detect attempts to exploit this buffer overflow. 9. Regularly audit router configurations and firmware versions to ensure compliance with security best practices.