CVE-2025-7421 is a critical stack-based buffer overflow vulnerability identified in the Tenda O3V2 device, specifically version 1.0.0.12(3880). The flaw exists in the httpd component, within the fromMacFilterModify function of the /goform/operateMacFilter endpoint. The vulnerability arises due to improper handling and validation of the 'mac' argument, which allows an attacker to overflow the stack buffer. This overflow can lead to arbitrary code execution or cause a denial of service by crashing the device. The vulnerability is remotely exploitable without requiring user interaction or prior authentication, making it highly dangerous. The CVSS v4.0 score is 8.7 (high severity), reflecting the ease of exploitation (network attack vector, low complexity), lack of required privileges or user interaction, and the high impact on confidentiality, integrity, and availability. Although no public exploits have been observed in the wild yet, the exploit code has been disclosed publicly, increasing the risk of imminent attacks. The vulnerability affects a specific firmware version of the Tenda O3V2, a device commonly used for wireless networking, often in small office or home office environments. The stack-based buffer overflow can be leveraged by attackers to gain control over the device, potentially allowing them to intercept or manipulate network traffic, pivot into internal networks, or disrupt network availability.

For European organizations, the impact of this vulnerability can be significant, especially for small and medium-sized enterprises (SMEs) and home office users relying on Tenda O3V2 devices for network connectivity. Exploitation could lead to unauthorized access to internal networks, interception of sensitive data, or disruption of business operations through denial of service. Given the device’s role as a network gateway, compromise could facilitate lateral movement within corporate networks, jeopardizing confidentiality and integrity of data. Critical infrastructure sectors that depend on reliable network connectivity could face operational disruptions. Additionally, the lack of authentication requirement and remote exploitability increases the risk of widespread attacks, potentially affecting organizations that have not updated or patched their devices. The public disclosure of exploit code further elevates the threat level, as less sophisticated attackers may leverage it to conduct attacks. The vulnerability also poses risks to privacy and compliance with European data protection regulations if personal or sensitive data is exposed due to network compromise.

1. Immediate firmware upgrade: Organizations should verify if Tenda has released a patched firmware version for the O3V2 device and apply it promptly. 2. Network segmentation: Isolate vulnerable devices from critical network segments to limit potential lateral movement in case of compromise. 3. Access control: Restrict remote management interfaces and disable unnecessary services on the device to reduce attack surface. 4. Monitoring and detection: Implement network monitoring to detect unusual traffic patterns or attempts to exploit the /goform/operateMacFilter endpoint. 5. Device replacement: For environments where patching is not feasible or devices are end-of-life, consider replacing Tenda O3V2 devices with more secure alternatives. 6. Vendor engagement: Engage with Tenda support channels to obtain official patches or mitigation guidance and report any suspicious activity. 7. Incident response readiness: Prepare to respond to potential exploitation incidents by having updated backups and a response plan focused on network device compromise. These steps go beyond generic advice by emphasizing immediate patching, network architecture adjustments, and active monitoring tailored to the specific vulnerable component and attack vector.