CVE-2025-7855 is a critical security vulnerability identified in the Tenda FH451 router, specifically version 1.0.0.9. The flaw exists in the function 'fromqossetting' within the '/goform/qossetting' endpoint. This vulnerability arises due to improper handling of the 'page' argument, which leads to a stack-based buffer overflow. A stack-based buffer overflow occurs when data exceeding the buffer's capacity is written to the stack, potentially overwriting adjacent memory and control data such as return addresses. This can allow an attacker to execute arbitrary code remotely without authentication or user interaction, as the attack vector is network accessible (AV:N) and requires no privileges (PR:L) or user interaction (UI:N). The CVSS 4.0 base score of 8.7 reflects the high severity, with high impact on confidentiality, integrity, and availability (VC:H, VI:H, VA:H). The vulnerability does not require user interaction or elevated privileges, making exploitation easier. Although no known exploits are currently reported in the wild, the nature of the vulnerability and its remote exploitability make it a significant risk. The absence of a patch link indicates that a fix may not yet be publicly available, increasing the urgency for mitigation and monitoring. The vulnerability affects a specific firmware version (1.0.0.9), so devices running this version are at risk. Attackers could leverage this flaw to gain full control over affected devices, potentially using them as entry points into internal networks or for launching further attacks such as lateral movement or denial of service.

For European organizations, the impact of CVE-2025-7855 can be substantial. Tenda routers like the FH451 are commonly used in small to medium-sized enterprises and residential environments. Compromise of these devices could lead to unauthorized access to internal networks, interception or manipulation of sensitive data, disruption of network services, and potential pivoting to other critical infrastructure. Given the high impact on confidentiality, integrity, and availability, attackers could exfiltrate sensitive corporate information, inject malicious configurations, or cause network outages. This is particularly concerning for sectors with strict data protection requirements such as finance, healthcare, and government agencies within Europe. Additionally, the remote exploitability without authentication increases the risk of widespread automated attacks or targeted campaigns. The lack of current known exploits does not diminish the threat, as proof-of-concept exploits could emerge rapidly once the vulnerability details are public. Organizations relying on Tenda FH451 routers must consider the risk of supply chain compromise and the potential for attackers to use these devices as footholds in their networks.

1. Immediate Inventory and Version Verification: Organizations should identify all Tenda FH451 devices in their environment and verify firmware versions. Devices running version 1.0.0.9 are vulnerable. 2. Firmware Updates: Monitor Tenda’s official channels for firmware updates addressing CVE-2025-7855 and apply patches promptly once available. 3. Network Segmentation: Isolate vulnerable devices from critical network segments to limit potential lateral movement if compromised. 4. Access Controls: Restrict remote management interfaces of Tenda FH451 routers to trusted IP addresses and disable remote administration if not required. 5. Intrusion Detection and Prevention: Deploy network-based IDS/IPS solutions with signatures or anomaly detection capable of identifying exploitation attempts targeting the '/goform/qossetting' endpoint or unusual buffer overflow patterns. 6. Monitoring and Logging: Enable detailed logging on routers and network devices to detect suspicious activity related to QoS settings or unexpected requests to the vulnerable endpoint. 7. Temporary Workarounds: If patching is not immediately possible, consider firewall rules to block external access to the vulnerable endpoint or ports used by the router’s management interface. 8. Vendor Engagement: Engage with Tenda support for guidance and timelines on patch releases and consider alternative hardware if risk tolerance is low. 9. Employee Awareness: Inform IT and security teams about the vulnerability to ensure rapid response to any detected exploitation attempts.