CVE-2025-12259 is a stack-based buffer overflow vulnerability identified in the TOTOLINK A3300R router firmware version 17.0.0cu.557_B20221024. The vulnerability resides in the setScheduleCfg function of the /cgi-bin/cstecgi.cgi CGI script, which processes POST requests. Specifically, the flaw is triggered by improper handling of the 'recHour' POST parameter, where crafted input can overflow a stack buffer. This overflow can lead to arbitrary code execution or cause the device to crash, resulting in denial of service. The vulnerability is remotely exploitable without requiring authentication or user interaction, making it highly dangerous. The CVSS v4.0 score of 8.7 reflects its high severity, with an attack vector of network (remote), low attack complexity, no privileges or user interaction required, and high impact on confidentiality, integrity, and availability. Although no active exploitation has been reported, a public exploit is available, increasing the likelihood of attacks. The vulnerability affects a specific firmware version, so devices running this version or earlier are at risk. Exploitation could allow attackers to take control of the router, intercept or manipulate traffic, or disrupt network connectivity. The vulnerability highlights the risks of insecure CGI parameter handling in embedded device firmware.

For European organizations, exploitation of CVE-2025-12259 could lead to significant operational disruption and data compromise. Successful attacks may allow adversaries to execute arbitrary code on affected routers, potentially gaining control over network traffic, intercepting sensitive communications, or launching further attacks within the internal network. This could impact confidentiality by exposing sensitive data, integrity by allowing manipulation of network traffic or configurations, and availability by causing device crashes or network outages. Organizations relying on TOTOLINK A3300R routers in critical infrastructure, enterprise networks, or government environments face elevated risks. The remote and unauthenticated nature of the exploit increases the attack surface, especially for devices exposed to the internet or poorly segmented internal networks. The presence of a public exploit further raises the threat level, as less skilled attackers can leverage it. Disruption of network connectivity could affect business continuity, and unauthorized access could lead to data breaches or espionage. The impact is particularly acute for sectors with stringent data protection requirements under GDPR and other regulations.

1. Immediately identify and inventory all TOTOLINK A3300R devices running firmware version 17.0.0cu.557_B20221024 or earlier. 2. Apply official firmware updates or patches from TOTOLINK as soon as they become available to remediate the vulnerability. 3. Until patches are deployed, restrict remote access to the router management interface by disabling remote administration or limiting access to trusted IP addresses via firewall rules. 4. Implement network segmentation to isolate vulnerable devices from critical systems and sensitive data. 5. Monitor network traffic for unusual POST requests targeting /cgi-bin/cstecgi.cgi, especially those containing the 'recHour' parameter, using IDS/IPS or SIEM solutions. 6. Employ anomaly detection to identify potential exploitation attempts or device crashes. 7. Educate network administrators about the vulnerability and signs of compromise. 8. Consider replacing affected devices if patches are unavailable or if devices are no longer supported. 9. Regularly review and update device firmware as part of a robust patch management program. 10. Document and test incident response plans to quickly address potential exploitation events.