CVE-2018-5770 in AC15
Summary
by MITRE
An issue was discovered on Tenda AC15 devices. A remote, unauthenticated attacker can make a request to /goform/telnet, creating a telnetd service on the device. This service is password protected; however, several default accounts exist on the device that are root accounts, which can be used to log in.
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Analysis
by VulDB Data Team • 01/15/2020
The vulnerability identified as CVE-2018-5770 affects Tenda AC15 wireless routers and represents a critical security flaw in network device management. This issue enables remote attackers to remotely activate a telnet daemon service on the affected device without requiring authentication credentials. The vulnerability stems from improper access controls within the device's web management interface, specifically through the /goform/telnet endpoint which allows arbitrary execution of commands to enable remote access services. The device's firmware fails to properly validate incoming requests to this endpoint, creating an attack vector that bypasses normal authentication mechanisms. This flaw falls under CWE-284 which addresses improper access control, specifically targeting the unauthorized enabling of remote services. The vulnerability demonstrates a fundamental weakness in the device's privilege management system where administrative functions can be triggered without proper authentication.
The technical implementation of this vulnerability involves exploiting a hardcoded endpoint within the router's web server that directly controls service activation. When an attacker sends a request to /goform/telnet, the device's firmware executes the telnetd service startup routine without verifying the requestor's credentials. While the service does require a password for access, the device contains multiple default root accounts with predictable credentials, making the exploitation straightforward. These default accounts often include common username/password combinations such as admin/admin or root/root which are well-documented in security databases. The vulnerability creates a persistent backdoor that allows attackers to establish remote access to the device's command-line interface, effectively providing full administrative control over the router's configuration and network traffic routing.
The operational impact of this vulnerability extends far beyond simple unauthorized access, creating significant risks for network security and privacy. Once an attacker gains access through this vulnerability, they can modify firewall rules, redirect traffic, monitor network communications, and potentially use the compromised router as a pivot point for attacking other devices on the local network. The telnet service provides a direct command-line interface that allows attackers to execute arbitrary commands on the device, including installing malicious firmware, modifying network configurations, or creating persistent access mechanisms. This vulnerability directly maps to ATT&CK technique T1059.005 which covers command and scripting interpreter for remote access, and T1021.001 which addresses remote services via telnet. The attack surface is particularly dangerous because routers serve as central network infrastructure components, making compromised devices ideal for launching broader network attacks or establishing persistent access points within networks.
Mitigation strategies for CVE-2018-5770 require immediate firmware updates from Tenda to address the authentication bypass vulnerability. Network administrators should disable unnecessary services including telnet and enable only SSH for secure remote administration. The device should be configured with strong, unique passwords for all administrative accounts, and default credentials should be changed immediately upon device deployment. Network segmentation and firewall rules should be implemented to restrict access to administrative interfaces to trusted IP addresses only. Regular security audits should verify that remote services are properly configured and that no unauthorized access mechanisms exist. Organizations should implement network monitoring to detect unusual traffic patterns that may indicate exploitation attempts. Additionally, the vulnerability highlights the importance of secure device configuration practices and the necessity of regularly updating firmware to address known security flaws. The vulnerability demonstrates the critical importance of proper access control implementation and the need for vendors to properly validate all incoming requests to administrative interfaces.