CVE-2022-40861 is a high-severity stack overflow vulnerability identified in the Tenda AC18 router firmware version V15.03.05.19. The flaw exists within the function formSetQosBand->FUN_0007db78, which processes requests sent to the /goform/SetNetControlList/ endpoint. A stack overflow occurs when the function improperly handles input data, allowing an attacker to overwrite parts of the stack memory. This can lead to arbitrary code execution, denial of service, or other malicious outcomes. The vulnerability has a CVSS v3.1 base score of 7.2, indicating a high impact with network attack vector (AV:N), low attack complexity (AC:L), but requiring high privileges (PR:H) and no user interaction (UI:N). The scope is unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). No public exploits are currently known in the wild, and no official patches have been linked yet. The vulnerability is categorized under CWE-787 (Out-of-bounds Write), a common and dangerous class of memory corruption bugs. Given the nature of the vulnerability, an attacker with high privileges on the device's network interface could exploit this flaw remotely to gain control over the router or disrupt its operation.

For European organizations, especially those relying on Tenda AC18 routers for network connectivity, this vulnerability poses a significant risk. Exploitation could lead to full compromise of the router, enabling attackers to intercept, manipulate, or disrupt network traffic. This could result in data breaches, loss of network availability, or serve as a foothold for lateral movement within corporate networks. The high impact on confidentiality, integrity, and availability means sensitive organizational data and critical services could be jeopardized. Small and medium enterprises or branch offices using this router model without robust network segmentation or monitoring are particularly vulnerable. Additionally, compromised routers could be leveraged in botnets or for launching further attacks, amplifying the threat landscape in Europe. The lack of a patch increases the urgency for organizations to implement interim mitigations to reduce exposure.

Given the absence of an official patch, European organizations should take immediate steps to mitigate risk. First, restrict access to the router management interface, especially the /goform/SetNetControlList/ endpoint, by limiting it to trusted internal networks and disabling remote management if enabled. Implement strict network segmentation to isolate routers from critical infrastructure and sensitive data environments. Monitor network traffic for unusual activity or signs of exploitation attempts targeting the router. Where possible, upgrade or replace affected Tenda AC18 routers with models that have received security updates or are known to be secure. Employ intrusion detection/prevention systems (IDS/IPS) with signatures or heuristics capable of detecting exploitation attempts targeting this vulnerability. Finally, maintain an inventory of affected devices and stay alert for vendor advisories or patches to apply updates promptly once available.