Executive Summary

CVE-2026-5102 is a command injection vulnerability in the TOTOLINK A3300R router, version 17.0.0cu.557_b20221024. It affects the function setSmartQosCfg in the /cgi-bin/cstecgi.cgi component, specifically through the manipulation of the qos_up_bw parameter.

When a specially crafted value is supplied to qos_up_bw, it is formatted into a buffer and then executed as a system command by the router. This allows an attacker to remotely execute arbitrary operating system commands on the device.

The vulnerability can be exploited by sending a crafted POST request to the router's web interface, causing it to run commands such as downloading malicious files from an attacker-controlled server.

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Impact Analysis

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

• Attackers can take control of the router, potentially altering its configuration or using it as a foothold to access other devices on the network.
• It can lead to unauthorized data access, interception, or disruption of network services.
• The router could be used to download and execute malicious payloads, leading to further compromise.

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Detection Guidance

This vulnerability can be detected by monitoring for suspicious POST requests to the endpoint /cgi-bin/cstecgi.cgi that include the parameter qos_up_bw with unusual or command-like values.

A practical detection method is to capture and analyze HTTP traffic targeting the affected router, looking for POST requests containing the qos_up_bw parameter with embedded commands.

For example, using a network packet capture tool like tcpdump or Wireshark, you can filter for HTTP POST requests to /cgi-bin/cstecgi.cgi and inspect the payload for suspicious qos_up_bw values.

• tcpdump -i <interface> -A -s 0 'tcp port 80 and (((ip dst <router_ip>) and (tcp[((tcp[12:1] & 0xf0) >> 2):4] = 0x504f5354))' # Capture HTTP POST packets to the router
• Use curl or similar tools to test the endpoint with crafted payloads to see if the router executes commands, e.g.: curl -X POST http://<router_ip>/cgi-bin/cstecgi.cgi -d 'qos_up_bw=;id;'

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Mitigation Strategies

Immediate mitigation steps include restricting access to the affected router's management interface to trusted networks only, such as limiting access via firewall rules or network segmentation.

Disable or block remote access to the /cgi-bin/cstecgi.cgi endpoint if possible, to prevent exploitation of the command injection vulnerability.

Monitor network traffic for suspicious POST requests containing the qos_up_bw parameter and respond to any detected exploitation attempts.

Apply any available firmware updates or patches from the vendor that address this vulnerability as soon as they become available.

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Compliance Impact

The vulnerability allows remote attackers to execute arbitrary system commands on the affected TOTOLINK A3300R router. This can lead to unauthorized access, data manipulation, or disruption of services.

Such unauthorized access and potential data breaches can impact compliance with common standards and regulations like GDPR and HIPAA, which require protection of personal and sensitive data against unauthorized access and cyberattacks.

Exploitation of this vulnerability could result in exposure or compromise of personal data, thereby violating data protection requirements and potentially leading to legal and regulatory consequences.

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