Can you explain this vulnerability to me?

CVE-2025-67445 is a denial-of-service vulnerability in the TOTOLINK X5000R router firmware version V9.1.0cu.2415. It affects the web management interface, specifically the CGI endpoint /cgi-bin/cstecgi.cgi.

The vulnerability arises because the CGI handler reads the CONTENT_LENGTH HTTP header, which is user-controlled, and allocates memory based on this value without sufficient bounds checking. Additionally, the Lighttpd web server configuration does not enforce a maximum request size limit because the relevant setting is commented out.

An attacker on the local network can send a crafted large POST request with an excessively large CONTENT_LENGTH value, causing the device to attempt to allocate more memory than it has available (256MB RAM). This leads to memory exhaustion and a segmentation fault, crashing the web management service and causing a denial of service.

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How can this vulnerability impact me? :

[{'type': 'paragraph', 'content': "This vulnerability can cause the TOTOLINK X5000R router's web management interface to crash, resulting in a denial of service."}, {'type': 'paragraph', 'content': "An attacker on the local area network can exploit this by sending a large, specially crafted POST request that exhausts the device's memory, causing the management CGI to crash and making the web interface unavailable."}, {'type': 'paragraph', 'content': 'This loss of availability can disrupt management and configuration of the router, potentially impacting network administration and security monitoring.'}] [1]

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How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:

I don't know

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How can this vulnerability be detected on my network or system? Can you suggest some commands?

[{'type': 'paragraph', 'content': "This vulnerability can be detected by sending a crafted large HTTP POST request to the vulnerable CGI endpoint /cgi-bin/cstecgi.cgi on the TOTOLINK X5000R router firmware version V9.1.0cu.2415. The request should include an excessively large CONTENT_LENGTH header and a large JSON payload, for example by inflating fields such as 'token' to increase the request size beyond safe limits."}, {'type': 'paragraph', 'content': 'A practical detection method is to use a command-line tool like curl or a custom Python script to send such a large POST request and observe if the device crashes or the web management interface becomes unavailable.'}, {'type': 'list_item', 'content': 'Example curl command to test the vulnerability (adjust payload size accordingly):'}, {'type': 'list_item', 'content': 'curl -X POST http://<target-ip>/cgi-bin/cstecgi.cgi -H "Content-Type: application/json" -H "Content-Length: <very_large_number>" -d \'{"token":"<very_large_string>"}\''}, {'type': 'paragraph', 'content': 'Alternatively, use the proof-of-concept Python script available in the referenced GitHub repository to automate the detection by sending a large POST request and monitoring the device response.'}] [1]

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What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation steps include restricting access to the vulnerable web management interface to trusted users only, preferably by limiting access to the LAN or specific IP addresses.

Additionally, monitor and block unusually large HTTP POST requests to the /cgi-bin/cstecgi.cgi endpoint using network security tools or firewall rules to prevent exploitation attempts.

If possible, update the device firmware to a version where the vulnerability is fixed or where the Lighttpd server enforces the maximum request size limit.

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