CVE-2021-47802: Tenda Router Config Download Vulnerability

CVE-2021-47802 Overview

CVE-2021-47802 is an authentication bypass vulnerability affecting Tenda D151 and D301 routers. The vulnerability allows remote attackers to retrieve sensitive router configuration files, including administrator credentials, without requiring any authentication. By sending a crafted request to the /goform/getimage endpoint, an attacker can download the complete router configuration, potentially gaining full administrative access to the device.

Critical Impact

Remote attackers can exfiltrate sensitive configuration data including admin credentials without authentication, enabling complete device compromise and potential network infiltration.

Affected Products

• Tenda D151 Router
• Tenda D301 Router

Discovery Timeline

• 2026-01-21 - CVE CVE-2021-47802 published to NVD
• 2026-01-21 - Last updated in NVD database

Technical Details for CVE-2021-47802

Vulnerability Analysis

This vulnerability is classified under CWE-306 (Missing Authentication for Critical Function). The Tenda D151 and D301 routers expose a sensitive endpoint at /goform/getimage that lacks proper authentication controls. This endpoint is designed to handle configuration image downloads but fails to verify whether the requesting party has appropriate authorization.

The attack can be executed remotely over the network without any user interaction or prior authentication. An attacker simply needs network access to the router's web interface to exploit this vulnerability. Once the configuration file is retrieved, it contains plaintext or easily decipherable administrator credentials, allowing the attacker to gain full administrative control over the router.

The impact is significant as it enables complete confidentiality breach of sensitive device configuration data. This type of vulnerability is particularly dangerous in IoT and network devices as they often sit at critical points in network infrastructure.

Root Cause

The root cause of this vulnerability is the absence of authentication mechanisms on the /goform/getimage endpoint. The router's web interface fails to implement proper access controls, allowing any remote user to access sensitive configuration retrieval functionality. This represents a fundamental design flaw where a critical administrative function was exposed without security constraints.

Attack Vector

The attack vector is network-based, requiring the attacker to have network connectivity to the router's management interface. The exploitation process involves sending an HTTP request to the vulnerable endpoint to retrieve the configuration file. No authentication credentials, user interaction, or special privileges are required.

The attack exploits the /goform/getimage endpoint which returns the router's configuration data. This configuration typically includes sensitive information such as administrator usernames and passwords, WiFi credentials, network settings, and other device-specific configurations. With this information, an attacker can authenticate to the router's administrative interface and gain full control over the device.

For detailed technical information about this vulnerability, refer to the Exploit-DB entry #49782 and the VulnCheck Advisory.

Detection Methods for CVE-2021-47802

Indicators of Compromise

• Unexpected HTTP requests to /goform/getimage from external or unknown IP addresses
• Multiple rapid requests to the configuration download endpoint
• Access logs showing successful downloads of configuration images by unauthenticated sessions
• Configuration file access from IP addresses outside of expected administrative ranges

Detection Strategies

• Monitor HTTP access logs for requests targeting /goform/getimage endpoint
• Implement network intrusion detection rules to alert on attempts to access the vulnerable endpoint
• Review router access logs for any successful configuration downloads
• Deploy network monitoring to identify suspicious traffic patterns to router management interfaces

Monitoring Recommendations

• Enable comprehensive logging on the router management interface if supported
• Implement network segmentation to isolate router management interfaces from untrusted networks
• Use a SIEM solution to correlate and alert on suspicious endpoint access patterns
• Periodically audit network traffic to identify potential exploitation attempts

How to Mitigate CVE-2021-47802

Immediate Actions Required

• Restrict network access to the router's web management interface using firewall rules
• Ensure the router management interface is not exposed to the internet or untrusted networks
• Change all administrative credentials immediately, assuming they may have been compromised
• Consider replacing affected devices with models that receive regular security updates

Patch Information

No vendor patch information is currently available for this vulnerability. Tenda has not released a security update to address this issue. Organizations using affected devices should implement network-based mitigations and consider replacing vulnerable hardware with actively supported alternatives. For vendor information, visit the Tenda Official Website.

Workarounds

• Implement strict firewall rules to block external access to the router's management interface
• Place the router behind a network firewall or VPN that requires authentication before accessing management functions
• If possible, disable the web management interface entirely and use alternative management methods
• Segment network traffic to ensure the management interface is only accessible from a dedicated administrative VLAN

# Example firewall rule to restrict management interface access
# Block external access to router management interface (adjust IP ranges as needed)
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP