The D-Link DIR-825 Rev.B router firmware version 2.10 and earlier contains a stack-based buffer overflow vulnerability in the apply.cgi endpoint, specifically triggered by the countdown_time POST parameter. This vulnerability (CVE-2025-10666) allows an attacker to send an overly long string (e.g., 4000 characters) in the countdown_time parameter, which overflows the stack buffer and crashes the router’s web management process. The exploit causes a denial-of-service (DoS) condition by making the router unresponsive or forcing a reboot. The vulnerability does not require authentication or user interaction but does require network access to the router’s management interface, typically accessible only from the local network. The exploit code is publicly available in Python, demonstrating how to send the malicious POST request to the router’s apply.cgi endpoint. This vulnerability affects physical hardware running the vulnerable firmware and can disrupt network availability. No official patch or firmware update link is currently provided, increasing the urgency for network administrators to implement compensating controls. The exploit’s ease of use and the critical role of routers in network infrastructure make this a significant threat for organizations relying on this device. The lack of known active exploitation in the wild suggests it is not yet widely weaponized, but the presence of public exploit code lowers the barrier for attackers.

For European organizations, exploitation of this vulnerability can lead to temporary or prolonged loss of internet connectivity and internal network disruption, impacting business operations, communications, and access to cloud services. Small and medium-sized businesses (SMBs) and home office environments using the D-Link DIR-825 Rev.B router are particularly vulnerable due to the device’s common use in these segments. The DoS condition can be exploited by insiders or attackers who gain local network access, potentially as part of a broader attack chain. Critical infrastructure or enterprises relying on this router model for network edge connectivity may experience operational downtime, affecting productivity and service availability. The inability to authenticate or require user interaction lowers the complexity of exploitation, increasing risk. The absence of a patch means organizations must rely on network segmentation, access controls, or device replacement to mitigate impact. The disruption caused by the DoS can also be leveraged as a diversion tactic for other attacks.

1. Immediately restrict access to the router’s management interface (apply.cgi endpoint) to trusted IP addresses only, preferably via firewall rules or VLAN segmentation. 2. Disable remote management features if enabled, to prevent exploitation from outside the local network. 3. Monitor network traffic for unusual POST requests targeting the apply.cgi endpoint with abnormally large parameters. 4. Replace or upgrade routers running firmware version 2.10 or earlier to newer, patched models or firmware versions once available. 5. If firmware updates are unavailable, consider deploying network-level DoS protection appliances or intrusion prevention systems (IPS) that can detect and block exploit attempts. 6. Educate network administrators and users about the vulnerability and the importance of securing router management interfaces. 7. Regularly audit network devices to identify vulnerable models and firmware versions. 8. Implement network segmentation to isolate critical systems from devices that may be vulnerable to exploitation.