CVE-2025-5863 is a critical security vulnerability identified in the Tenda AC5 router, specifically in firmware version 15.03.06.47. The flaw exists in the function formSetRebootTimer within the /goform/SetRebootTimer endpoint. This vulnerability is a stack-based buffer overflow triggered by improper handling of the rebootTime argument. An attacker can remotely send a specially crafted request to this endpoint, causing the buffer overflow condition. This can lead to arbitrary code execution on the device without requiring user interaction or authentication, as indicated by the CVSS vector (AV:N/AC:L/AT:N/UI:N/PR:L). The vulnerability affects the confidentiality, integrity, and availability of the device, potentially allowing attackers to take full control of the router, intercept or manipulate network traffic, or disrupt network services. The exploit has been publicly disclosed, increasing the risk of exploitation, although no confirmed exploits in the wild have been reported yet. The CVSS 4.0 base score of 8.7 classifies this as a high-severity issue, reflecting the ease of exploitation and the critical impact on affected devices. The vulnerability does not require user interaction but does require low privileges (PR:L), which typically means an attacker needs to be on the local network or have some level of access to the device's management interface. However, since the attack vector is network-based (AV:N), remote exploitation is feasible, especially if the device is exposed to the internet or an untrusted network. The lack of available patches at the time of disclosure increases the urgency for mitigation and risk management by affected users and organizations.

For European organizations, the impact of this vulnerability can be significant. Tenda AC5 routers are commonly used in small to medium-sized enterprises and home office environments, which are prevalent across Europe. Successful exploitation could allow attackers to gain persistent control over network gateways, enabling interception of sensitive communications, insertion of malicious payloads, or disruption of network connectivity. This could lead to data breaches, loss of service, and compromise of internal network security. Given the critical nature of the vulnerability and the potential for remote exploitation without user interaction, attackers could leverage this flaw to establish footholds within corporate networks or disrupt critical business operations. The risk is heightened in organizations with limited IT security resources or those that have not implemented network segmentation or device hardening. Additionally, the exposure of such routers to the public internet or untrusted networks increases the attack surface. The vulnerability could also be exploited as part of larger botnet campaigns or ransomware attacks targeting European infrastructure, further amplifying its impact.

To mitigate this vulnerability, European organizations should first verify if they are using Tenda AC5 routers running firmware version 15.03.06.47. Immediate steps include: 1) Isolate affected devices from untrusted networks, especially the internet, by disabling remote management interfaces or applying strict firewall rules limiting access to trusted IP addresses. 2) Implement network segmentation to restrict the exposure of vulnerable routers to critical internal systems. 3) Monitor network traffic for unusual activity targeting the /goform/SetRebootTimer endpoint or anomalous reboot commands. 4) Contact Tenda support or check official channels regularly for firmware updates or patches addressing CVE-2025-5863 and apply them promptly once available. 5) As a temporary workaround, consider disabling or restricting access to the reboot timer functionality if configurable. 6) Employ intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics capable of detecting exploitation attempts targeting this vulnerability. 7) Educate IT staff about the vulnerability and ensure incident response plans include steps for handling potential exploitation. These measures go beyond generic advice by focusing on network-level controls, monitoring specific attack vectors, and emphasizing proactive isolation and segmentation to reduce risk until patches are available.