CVE-2024-39801 is a classic stack-based buffer overflow vulnerability classified under CWE-120, found in the Wavlink AC3000 router firmware version M33A8.V5030.210505. The flaw resides in the qos.cgi script's qos_settings() function, which processes HTTP POST requests related to Quality of Service (QoS) settings. Specifically, the vulnerability is triggered by the qos_bandwidth POST parameter, which is not properly bounds-checked before being copied into a fixed-size buffer on the stack. An attacker with valid authentication credentials can craft a malicious HTTP request that overflows the buffer, overwriting the stack and potentially allowing arbitrary code execution with elevated privileges. The vulnerability's CVSS 3.1 score of 9.1 reflects its critical nature, with network attack vector (AV:N), low attack complexity (AC:L), requiring high privileges (PR:H), no user interaction (UI:N), and complete impact on confidentiality, integrity, and availability (C:H/I:H/A:H). Although no public exploits have been observed in the wild, the vulnerability poses a severe risk due to the potential for remote code execution and full device compromise. The vulnerability affects only the specified firmware version, and no official patches have been linked yet. The attack surface includes any network-exposed management interface where authenticated HTTP requests can be sent. This vulnerability could be leveraged to pivot into internal networks or disrupt network operations.

For European organizations, the impact of this vulnerability can be significant. Wavlink AC3000 routers are used in small to medium enterprise and possibly home office environments, which are common in Europe. Exploitation could lead to complete compromise of the affected device, allowing attackers to intercept, modify, or disrupt network traffic, degrade service availability, or use the device as a foothold for lateral movement within corporate networks. Critical infrastructure operators, government agencies, and businesses relying on these routers for network segmentation or QoS enforcement could face data breaches, operational disruptions, or espionage risks. The requirement for authentication limits exploitation to insiders or attackers who have obtained credentials, but phishing or credential theft could enable this. The lack of patches increases the window of exposure. Given the interconnected nature of European networks and regulatory requirements for data protection (e.g., GDPR), such a compromise could also lead to compliance violations and reputational damage.

Organizations should immediately audit their networks to identify any Wavlink AC3000 devices running the vulnerable firmware version M33A8.V5030.210505. Until a patch is available, restrict access to the router's management interface by implementing network segmentation and firewall rules to limit HTTP access to trusted administrators only. Enforce strong authentication mechanisms and change default or weak passwords to reduce the risk of credential compromise. Monitor network traffic and device logs for unusual activity indicative of exploitation attempts. Disable QoS management interfaces if not required or restrict their usage. Consider deploying network intrusion detection systems (IDS) with signatures tuned to detect anomalous HTTP POST requests targeting qos.cgi. Engage with Wavlink support channels to obtain firmware updates or security advisories. For critical environments, consider replacing vulnerable devices with models from vendors with faster security response capabilities. Regularly back up device configurations and ensure incident response plans include scenarios involving router compromise.