CVE-2025-7855 is a critical stack-based buffer overflow vulnerability identified in the Tenda FH451 router, specifically affecting firmware version 1.0.0.9. The vulnerability resides in the function 'fromqossetting' within the '/goform/qossetting' endpoint. An attacker can exploit this flaw by manipulating the 'page' argument sent to this function, causing a stack-based buffer overflow. This type of vulnerability allows an attacker to overwrite parts of the stack memory, potentially leading to arbitrary code execution, denial of service, or system crashes. The vulnerability is remotely exploitable without requiring user interaction or authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The CVSS 4.0 base score is 8.7, categorizing it as a high-severity issue. The vulnerability impacts confidentiality, integrity, and availability with high impact metrics, and the attack complexity is low, making exploitation feasible for attackers with limited privileges. No known exploits are currently reported in the wild, and no patches or mitigation links have been published yet. The absence of a patch increases the urgency for affected users to implement interim mitigations or monitor for updates from the vendor. Given the nature of the vulnerability and the device type, successful exploitation could allow attackers to gain control over the router, intercept or manipulate network traffic, and potentially pivot to internal networks, posing significant security risks.

For European organizations, this vulnerability poses a significant threat, especially for those relying on Tenda FH451 routers in their network infrastructure. Compromise of these routers could lead to unauthorized access to internal networks, interception of sensitive data, disruption of network services, and potential lateral movement to other critical systems. Small and medium enterprises (SMEs) and home office setups using this device are particularly vulnerable due to typically less stringent network security controls. The impact extends to confidentiality breaches through traffic interception, integrity violations via manipulation of network configurations, and availability issues from denial-of-service conditions caused by exploitation. Additionally, critical sectors such as finance, healthcare, and government entities using these routers could face severe operational disruptions and data breaches, leading to regulatory non-compliance and reputational damage. The remote and unauthenticated nature of the exploit increases the risk of widespread attacks, especially if automated exploit tools emerge. The lack of current known exploits provides a window for proactive defense but also means organizations must remain vigilant for emerging threats.

Given the absence of an official patch, European organizations should implement immediate compensating controls. These include isolating affected Tenda FH451 devices from critical network segments and restricting remote management access via firewall rules or network segmentation. Disabling or restricting access to the '/goform/qossetting' endpoint, if feasible, can reduce attack surface. Network intrusion detection systems (NIDS) should be configured to monitor and alert on suspicious traffic patterns targeting the vulnerable endpoint or unusual POST requests containing the 'page' parameter. Organizations should conduct thorough inventories to identify all Tenda FH451 devices and prioritize their replacement or firmware upgrade once patches become available. Employing network-level protections such as VPNs and strong authentication for remote access can further mitigate risk. Regularly monitoring vendor advisories and threat intelligence feeds for updates or exploit releases is critical. Finally, organizations should consider deploying endpoint detection and response (EDR) solutions to detect potential lateral movement or post-exploitation activities stemming from compromised routers.