CVE-2020-36963: Intelbras RF 301K Auth Bypass Vulnerability

CVE-2020-36963 Overview

CVE-2020-36963 is an authentication bypass vulnerability affecting Intelbras Router RF 301K firmware version 1.1.2. This vulnerability allows unauthenticated attackers to download router configuration files by sending a specific HTTP GET request to /cgi-bin/DownloadCfg/RouterCfm.cfg. The flaw enables remote attackers to retrieve sensitive router configuration data without requiring any authentication credentials, potentially exposing network credentials, administrative passwords, and other sensitive configuration parameters.

Critical Impact

Unauthenticated remote attackers can extract sensitive router configuration files containing credentials and network settings, enabling further network compromise and lateral movement.

Affected Products

• Intelbras Router RF 301K firmware version 1.1.2

Discovery Timeline

• 2026-01-28 - CVE CVE-2020-36963 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2020-36963

Vulnerability Analysis

This vulnerability is classified under CWE-306 (Missing Authentication for Critical Function). The Intelbras Router RF 301K contains a critical flaw where the configuration file download endpoint lacks proper authentication checks. The /cgi-bin/DownloadCfg/RouterCfm.cfg endpoint is exposed to the network and does not validate whether the requesting user has been properly authenticated before serving the router's configuration file.

The configuration file typically contains highly sensitive information including administrative credentials, WiFi passwords, PPPoE authentication details, and network topology information. An attacker with network access to the router's management interface can retrieve this file without any authentication, leading to complete compromise of the router and potentially the broader network.

Root Cause

The root cause of this vulnerability is the absence of authentication validation on the configuration file download endpoint. The web server component of the router firmware fails to check for a valid session or credentials before processing requests to the /cgi-bin/DownloadCfg/RouterCfm.cfg path. This is a design flaw where a critical administrative function was inadvertently left unprotected.

Attack Vector

The attack vector is network-based and requires no user interaction or authentication. An attacker can exploit this vulnerability by simply sending an HTTP GET request to the vulnerable endpoint. The attack can be performed from the local network if the router's management interface is accessible on the LAN, or remotely if the management interface is exposed to the internet.

The exploitation is trivial - an attacker simply needs to navigate to or request the vulnerable URL path, and the router will return the complete configuration file. This file can then be parsed to extract administrative credentials, network configurations, and other sensitive data that can be used for further attacks.

For technical details and proof-of-concept information, see the Exploit-DB #49126 entry and the VulnCheck Advisory on Intelbras Router.

Detection Methods for CVE-2020-36963

Indicators of Compromise

• HTTP GET requests to /cgi-bin/DownloadCfg/RouterCfm.cfg from unauthorized sources
• Unusual access patterns to the router's web management interface from external or unexpected IP addresses
• Network traffic containing router configuration file contents in HTTP responses
• Authentication failures or configuration changes following unexplained configuration file access

Detection Strategies

• Monitor web server access logs on the router for requests to /cgi-bin/DownloadCfg/RouterCfm.cfg
• Deploy network intrusion detection signatures to alert on requests containing the vulnerable endpoint path
• Implement network traffic analysis to detect configuration file exfiltration patterns
• Review firewall logs for unexpected connections to the router management interface from untrusted networks

Monitoring Recommendations

• Enable logging on the router if supported and regularly review access logs for suspicious activity
• Implement network segmentation to isolate router management interfaces from untrusted network segments
• Use a Security Information and Event Management (SIEM) solution to correlate access attempts across multiple network devices
• Consider deploying network detection tools capable of identifying authentication bypass attempts on IoT and network devices

How to Mitigate CVE-2020-36963

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only using firewall rules
• Disable remote management if not required to reduce the attack surface
• Check for firmware updates from Intelbras that may address this vulnerability
• Monitor network traffic for signs of exploitation and review configuration files for unauthorized changes

Patch Information

Users should check the Intelbras Official Website for firmware updates that address this vulnerability. If a patched firmware version is available, update immediately following the manufacturer's guidelines. Prior to updating, back up the current router configuration and verify the integrity of the new firmware.

Workarounds

• Implement access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Place the router's management interface on a separate VLAN that is not accessible from untrusted networks
• If possible, disable the web-based management interface entirely and use alternative management methods
• Deploy a firewall or reverse proxy in front of the router to filter requests to the vulnerable endpoint

# Example iptables rules to restrict management interface access
# Allow management access only from trusted admin workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP

# Block access to the vulnerable endpoint specifically (if supported by firewall)
iptables -A INPUT -p tcp --dport 80 -m string --string "/cgi-bin/DownloadCfg/RouterCfm.cfg" --algo bm -j DROP