CVE-2025-7796 is a critical stack-based buffer overflow vulnerability identified in the Tenda FH451 router, specifically in firmware version 1.0.0.9. The flaw exists in the fromPptpUserAdd function within the /goform/PPTPDClient endpoint. This function improperly handles the 'Username' argument, allowing an attacker to craft input that overflows the stack buffer. Such a vulnerability can be exploited remotely without requiring user interaction or prior authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The overflow can lead to arbitrary code execution with high impact on confidentiality, integrity, and availability of the device. Although no public exploits are currently known to be in the wild, the exploit code has been disclosed, increasing the risk of imminent attacks. The vulnerability's CVSS 4.0 score of 8.7 reflects its high severity, driven by the ease of remote exploitation and the critical nature of the affected device. The Tenda FH451 is a consumer and small office/home office (SOHO) router, often deployed in residential and small business environments, which may lack robust security monitoring. The vulnerability could be leveraged by attackers to gain persistent control over the router, intercept or manipulate network traffic, or pivot into internal networks. Given the lack of available patches at the time of disclosure, affected devices remain vulnerable until firmware updates are released and applied.

For European organizations, especially small businesses and home offices relying on Tenda FH451 routers, this vulnerability poses a significant risk. Compromise of these routers can lead to interception of sensitive communications, unauthorized network access, and potential lateral movement into corporate networks if the router is used as a gateway device. The ability to execute arbitrary code remotely without authentication increases the attack surface, potentially enabling attackers to deploy malware, create botnets, or exfiltrate data. In sectors with strict data protection regulations like GDPR, such breaches could result in regulatory penalties and reputational damage. Additionally, critical infrastructure or teleworking setups using these routers may face service disruptions or espionage risks. The widespread use of Tenda devices in certain European markets amplifies the potential impact, especially where IT security resources are limited and patch management is slow.

Immediate mitigation steps include disabling the PPTP client functionality if not required, as this is the vulnerable service entry point. Network administrators should implement strict firewall rules to block external access to the /goform/PPTPDClient endpoint and monitor network traffic for unusual activity targeting this interface. Segmentation of the network to isolate vulnerable routers from sensitive internal systems can reduce risk. Since no official patches are currently available, organizations should contact Tenda support for firmware updates or advisories and apply them promptly once released. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for this vulnerability can help detect exploitation attempts. Additionally, organizations should conduct asset inventories to identify all Tenda FH451 devices and consider replacing unsupported or unpatchable units with more secure alternatives. Regular security awareness training for users to recognize suspicious network behavior is also recommended.