CVE-2025-67445 is a denial-of-service (DoS) vulnerability identified in the TOTOLINK X5000R router firmware version V9.1.0cu.2415_B20250515. The vulnerability resides in the /cgi-bin/cstecgi.cgi management CGI script, which processes HTTP POST requests. Specifically, the CGI reads the CONTENT_LENGTH environment variable and uses it to allocate memory via malloc(CONTENT_LENGTH + 1) without performing sufficient bounds checking or validation on the size value. If the lighttpd web server, which hosts the CGI, does not enforce a request size limit, an attacker can send an excessively large POST request. This leads to memory exhaustion or a segmentation fault in the CGI process, causing it to crash. The crash results in the loss of availability of the router’s web management interface, effectively denying legitimate users access to device management functions. The vulnerability does not require authentication or user interaction beyond sending a crafted HTTP POST request to the affected endpoint. No patches or updates are currently linked, and no known exploits have been reported in the wild as of the publication date. The root cause is improper input validation and lack of resource management in the CGI script combined with insufficient server-side request size enforcement.

The primary impact of CVE-2025-67445 is a denial-of-service condition that disrupts access to the TOTOLINK X5000R router’s web management interface. This can prevent administrators from managing or configuring the device remotely, potentially delaying incident response or routine maintenance. In environments where these routers are deployed as critical network infrastructure, such as enterprise networks, small to medium businesses, or service provider edge devices, this loss of availability could lead to broader network outages or degraded service quality. Attackers could exploit this vulnerability to cause repeated crashes, leading to persistent denial of management access. Although the vulnerability does not directly compromise confidentiality or integrity, the inability to manage the device could indirectly increase risk exposure by preventing timely security updates or configuration changes. The ease of exploitation—requiring only an HTTP POST request—and lack of authentication requirements increase the threat level. However, the impact is limited to devices running the specific vulnerable firmware version and having misconfigured or unenforced request size limits on the lighttpd server.

To mitigate CVE-2025-67445, organizations should first verify if their TOTOLINK X5000R routers are running the vulnerable firmware version V9.1.0cu.2415_B20250515. If so, they should monitor for firmware updates or patches from TOTOLINK and apply them promptly once available. In the interim, administrators should enforce strict request size limits on the lighttpd web server hosting the management CGI to prevent oversized POST requests from being processed. This can be done by configuring the server’s request size parameters to a safe maximum that aligns with expected legitimate traffic. Additionally, restricting access to the router’s management interface to trusted IP addresses or via VPN can reduce exposure to external attackers. Network-level protections such as web application firewalls (WAFs) or intrusion prevention systems (IPS) can be configured to detect and block abnormally large POST requests targeting the /cgi-bin/cstecgi.cgi endpoint. Regular monitoring of router logs for unusual request patterns and implementing rate limiting can further reduce risk. Finally, organizations should consider segmenting management interfaces away from public networks to limit attack surface.