CVE-2025-45790 is a medium-severity buffer overflow vulnerability identified in the TOTOLINK A3100R router firmware version V5.9c.1527. The vulnerability exists in the setMacQos interface within the /lib/cste_modules/firewall.so module. Specifically, the issue arises from improper handling of the 'priority' parameter, which can lead to a buffer overflow condition. Buffer overflow vulnerabilities occur when input data exceeds the allocated buffer size, potentially overwriting adjacent memory and enabling an attacker to execute arbitrary code or cause a denial of service. In this case, the vulnerability does not require any privileges (PR:N) or user interaction (UI:N) and can be exploited remotely over the network (AV:N). The CVSS v3.1 base score is 6.5, reflecting a medium severity with low complexity of attack and no authentication needed. The impact vector indicates limited confidentiality and integrity impact (C:L/I:L) but no availability impact (A:N). No known exploits are currently reported in the wild, and no patches have been published yet. The vulnerability is classified under CWE-121 (Stack-based Buffer Overflow), a common and well-understood software weakness. Exploitation could allow an attacker to manipulate QoS settings or potentially execute arbitrary code on the device, compromising the router's operation and network traffic management.

For European organizations, this vulnerability poses a risk primarily to those using TOTOLINK A3100R routers, which are typically deployed in small to medium business or home office environments. Successful exploitation could allow attackers to alter network traffic prioritization or gain unauthorized control over the router, potentially leading to interception or disruption of sensitive communications. While the direct impact on critical infrastructure may be limited due to the device's market segment, compromised routers can serve as entry points for lateral movement within corporate networks or as part of botnets for broader attacks. The confidentiality and integrity of network traffic could be undermined, affecting data privacy and trust. Additionally, the lack of available patches increases the window of exposure. European organizations with remote or distributed workforces relying on such routers should be particularly vigilant, as attackers can exploit the vulnerability remotely without authentication or user interaction.

Organizations should first inventory their network devices to identify any TOTOLINK A3100R routers running firmware version V5.9c.1527. Until an official patch is released, it is advisable to restrict network access to the router's management interfaces, ideally limiting them to trusted internal networks or VPNs. Network segmentation should be enforced to isolate vulnerable devices from critical systems. Monitoring network traffic for unusual QoS configuration changes or anomalous behavior can help detect exploitation attempts. Employing intrusion detection/prevention systems (IDS/IPS) with signatures for buffer overflow attempts targeting this interface may provide additional defense. If feasible, consider replacing affected routers with models from vendors with timely security support. Finally, maintain awareness of vendor advisories for patch releases and apply updates promptly once available.