CVE-2024-39802 is a classic stack-based buffer overflow vulnerability identified in the Wavlink AC3000 router firmware version M33A8.V5030.210505. The flaw resides in the qos.cgi script, specifically within the qos_settings() function that processes the qos_dat POST parameter. This parameter is not properly bounds-checked before being copied to a fixed-size buffer, allowing an attacker with authenticated HTTP access to send a specially crafted request that overflows the stack buffer. This overflow can overwrite the return address or other control data, enabling arbitrary code execution with elevated privileges on the device. The vulnerability is categorized under CWE-120 (Buffer Copy without Checking Size of Input), a well-known and dangerous class of memory corruption bugs. The CVSS v3.1 score of 9.1 reflects the vulnerability's 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 reported, the potential for exploitation is significant given the router’s role in network traffic management and the possibility of persistent device compromise. The vulnerability affects a specific firmware version, emphasizing the importance of firmware management and updates. The lack of available patches at the time of disclosure increases the urgency for interim mitigations.

For European organizations, exploitation of this vulnerability could lead to full compromise of affected Wavlink AC3000 routers, allowing attackers to intercept, modify, or disrupt network traffic. This can result in data breaches, network downtime, and lateral movement within corporate networks. Critical infrastructure operators and enterprises relying on these routers for Quality of Service (QoS) management may face severe operational disruptions. The confidentiality of sensitive communications could be compromised, and attackers might establish persistent footholds for further attacks. Given the router’s network position, the impact extends beyond individual devices to the broader organizational network, potentially affecting multiple connected systems. The requirement for authentication limits exposure but does not eliminate risk, especially in environments with weak credential management or insider threats. The critical severity underscores the need for immediate attention to prevent exploitation.

1. Immediately restrict access to the router’s management interface to trusted networks and users only, preferably via VPN or secure management VLANs. 2. Enforce strong authentication policies, including complex passwords and, if supported, multi-factor authentication for router access. 3. Monitor network traffic and device logs for unusual HTTP POST requests targeting qos.cgi or anomalous behavior indicative of exploitation attempts. 4. Disable QoS features or the qos.cgi interface if not essential, reducing the attack surface. 5. Maintain an inventory of all Wavlink AC3000 devices and verify firmware versions to identify vulnerable units. 6. Engage with Wavlink support channels to obtain and apply firmware updates or patches as soon as they become available. 7. Implement network segmentation to isolate critical devices and limit the spread of compromise. 8. Conduct regular security assessments and penetration tests focusing on network infrastructure devices. 9. Educate network administrators about this vulnerability and the importance of secure device management practices.