CVE-2020-10826: Draytek Vigor300b Firmware RCE Vulnerability

CVE-2020-10826 Overview

CVE-2020-10826 is a critical command injection vulnerability affecting DrayTek Vigor enterprise routers. The vulnerability exists in the /cgi-bin/activate.cgi endpoint on DrayTek Vigor3900, Vigor2960, and Vigor300B devices running firmware versions prior to 1.5.1. When DEBUG mode is enabled, remote attackers can achieve arbitrary command execution via specially crafted HTTP requests, potentially leading to complete device compromise.

Critical Impact

Unauthenticated remote attackers can execute arbitrary system commands on vulnerable DrayTek routers, enabling full device takeover, network pivoting, and persistent access to enterprise network infrastructure.

Affected Products

• DrayTek Vigor3900 (firmware versions before 1.5.1)
• DrayTek Vigor2960 (firmware versions before 1.5.1)
• DrayTek Vigor300B (firmware versions before 1.5.1)

Discovery Timeline

• 2020-03-26 - CVE-2020-10826 published to NVD
• 2025-05-05 - Last updated in NVD database

Technical Details for CVE-2020-10826

Vulnerability Analysis

This command injection vulnerability (CWE-77) affects the /cgi-bin/activate.cgi CGI script on DrayTek Vigor enterprise routers. The flaw allows remote attackers to inject and execute arbitrary operating system commands through maliciously crafted HTTP requests when the device is operating in DEBUG mode.

The vulnerability is particularly severe because it requires no authentication and can be exploited remotely over the network. Successful exploitation grants attackers the ability to execute commands with the privileges of the web server process, typically root on embedded devices, enabling complete control over the affected router.

Root Cause

The vulnerability stems from improper input validation in the activate.cgi CGI handler. When DEBUG mode is enabled, user-supplied input from HTTP request parameters is passed directly to system shell commands without adequate sanitization or escaping. This lack of input validation allows attackers to break out of the intended command context and inject arbitrary shell commands using common injection techniques such as command separators (;, |, &&, etc.).

Attack Vector

The attack is network-based and requires no user interaction or authentication. An attacker can exploit this vulnerability by sending a specially crafted HTTP request to the /cgi-bin/activate.cgi endpoint on a vulnerable DrayTek router. The malicious payload is embedded within HTTP request parameters and is processed by the CGI script when DEBUG mode is active.

The exploitation process involves:

1. Identifying a vulnerable DrayTek Vigor router with DEBUG mode enabled
2. Crafting an HTTP request to /cgi-bin/activate.cgi with command injection payload
3. The CGI script processes the request and passes unsanitized input to shell execution
4. Arbitrary commands execute with the privileges of the web server process

Due to the sensitive nature of this vulnerability, specific exploitation code is not provided. Security researchers should refer to the DrayTek Security Advisory and the Slashdot Vulnerability Overview for additional technical details.

Detection Methods for CVE-2020-10826

Indicators of Compromise

• Unusual HTTP requests targeting /cgi-bin/activate.cgi with malformed or suspicious parameters
• Unexpected outbound network connections from DrayTek routers to unknown destinations
• Unauthorized configuration changes or new user accounts on affected devices
• Evidence of command execution artifacts in router logs (shell metacharacters, encoded payloads)

Detection Strategies

• Monitor HTTP traffic to DrayTek devices for requests containing shell metacharacters (;, |, &&, $(), backticks) in URL parameters
• Implement web application firewall (WAF) rules to detect and block command injection patterns targeting CGI endpoints
• Deploy network intrusion detection signatures for known DrayTek exploitation patterns
• Audit router configurations to ensure DEBUG mode is disabled on all production devices

Monitoring Recommendations

• Enable comprehensive logging on DrayTek devices and forward logs to a centralized SIEM
• Establish baseline network behavior for router management interfaces and alert on anomalies
• Monitor for unexpected process spawning or file system modifications on affected devices
• Implement alerting for any access attempts to /cgi-bin/activate.cgi from external networks

How to Mitigate CVE-2020-10826

Immediate Actions Required

• Upgrade all affected DrayTek Vigor3900, Vigor2960, and Vigor300B devices to firmware version 1.5.1 or later immediately
• Disable DEBUG mode on all DrayTek routers in production environments
• Restrict administrative interface access to trusted internal networks only
• Implement network segmentation to isolate router management interfaces from untrusted networks

Patch Information

DrayTek has released firmware version 1.5.1 to address this command injection vulnerability. Administrators should download the patched firmware directly from the official DrayTek Security Advisory page and apply updates to all affected devices.

Workarounds

• Disable DEBUG mode on all affected devices if firmware updates cannot be applied immediately
• Block external access to the router's web management interface using firewall rules
• Implement access control lists (ACLs) to restrict management access to specific trusted IP addresses
• Consider placing vulnerable devices behind a reverse proxy with request filtering capabilities until patching is complete

# Example firewall rule to restrict management access (adjust for your environment)
# Block external access to DrayTek management interface
iptables -A INPUT -p tcp --dport 443 -s ! 10.0.0.0/8 -j DROP
iptables -A INPUT -p tcp --dport 80 -s ! 10.0.0.0/8 -j DROP