Compliance Impact

The vulnerability allows unauthorized attackers to enable the Telnet service on affected T3 Technology CPE devices without authentication. This unauthorized access could lead to potential exposure of sensitive configuration settings and network access, which may impact compliance with security requirements in common standards and regulations such as GDPR and HIPAA.

Specifically, enabling Telnet access without proper authentication increases the risk of unauthorized access to network devices, potentially leading to data breaches or unauthorized data processing. Such incidents could violate data protection and security obligations under regulations like GDPR and HIPAA that require appropriate access controls and protection of personal and sensitive data.

Remediation recommendations include enforcing authentication on all CGI endpoints, restricting access to the management interface via network segmentation, and monitoring for unauthorized Telnet activation, which are important steps to maintain compliance with these standards.

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Executive Summary

CVE-2026-35904 is a missing-authentication vulnerability in the web management interface of certain T3 Technology CPE devices. It allows an unauthorized attacker on the local network to enable the Telnet service by sending a specially crafted HTTP request to an unprotected CGI endpoint named telnetenable.cgi.

The vulnerability affects models including T625Pro, T6825G, and T7281. The endpoint simply toggles the Telnet service when the parameter "telnetenable=1" is provided, without executing any other supplied parameters.

Attackers can exploit this by sending a single HTTP GET request, either directly or via Blind CSRF from outside the local network. Once Telnet is enabled, attackers can authenticate using hardcoded credentials.

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Impact Analysis

This vulnerability allows unauthorized attackers to enable Telnet access on the affected devices, potentially exposing the device to remote login using hardcoded credentials.

Enabling Telnet access can lead to unauthorized configuration changes, loss of device control, and potential further compromise of the network where the device is deployed.

Because Telnet transmits data in plaintext, attackers could intercept sensitive information or use the device as a foothold for additional attacks.

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Detection Guidance

This vulnerability can be detected by monitoring for unauthorized activation of the Telnet service on affected T3 Technology CPE devices. Specifically, you can check if the Telnet service on port 23 has been enabled unexpectedly.

Detection can also involve inspecting HTTP requests to the device's web management interface for any crafted requests sent to the vulnerable CGI endpoint telnetenable.cgi with the parameter "telnetenable=1".

Suggested commands to detect Telnet service activation on the device or network include:

• On the device or network host, check if port 23 (Telnet) is open using: `netstat -an | grep ':23'` or `ss -tuln | grep ':23'`
• Scan the device IP for open Telnet port using: `nmap -p 23 <device_ip>`
• Monitor HTTP access logs or network traffic for GET requests to `/telnetenable.cgi?telnetenable=1` which indicate exploitation attempts.

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Mitigation Strategies

Immediate mitigation steps include enforcing authentication on all CGI endpoints of the affected devices to prevent unauthorized access.

Restrict access to the CPE management interface by implementing network segmentation, allowing only trusted and authenticated users to reach the device management interface.

Monitor the devices for any unauthorized activation of the Telnet service and disable Telnet if it is not required.

Since no vendor patch was provided at the time of disclosure, consider disabling the web management interface or restricting it to a secure management VLAN or VPN until a fix is available.

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