CVE-2021-46422: Telesquare SDT-CS3B1 Firmware RCE Flaw

CVE-2021-46422 Overview

CVE-2021-46422 is a critical OS command injection vulnerability affecting Telesquare SDT-CW3B1 firmware version 1.1.0. This vulnerability allows remote attackers to execute arbitrary operating system commands on the affected device without any authentication requirements. The unauthenticated nature of this vulnerability significantly increases its risk profile, as attackers can compromise devices directly from the network without needing valid credentials.

Critical Impact

Unauthenticated remote attackers can execute arbitrary OS commands on vulnerable Telesquare SDT-CW3B1 devices, potentially leading to complete device compromise, data exfiltration, and use of the device as a pivot point for further network attacks.

Affected Products

• Telesquare SDT-CW3B1 Firmware version 1.1.0
• Telesquare SDT-CS3B1 Hardware
• Telesquare SDT-CS3B1 Firmware

Discovery Timeline

• 2022-04-27 - CVE CVE-2021-46422 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2021-46422

Vulnerability Analysis

This vulnerability falls under CWE-78 (Improper Neutralization of Special Elements used in an OS Command), commonly known as OS Command Injection. The Telesquare SDT-CW3B1 router firmware version 1.1.0 fails to properly sanitize user-supplied input before passing it to system shell commands. This allows attackers to inject arbitrary commands that execute with the privileges of the web server process, typically root on embedded devices.

The vulnerability is particularly severe because it requires no authentication, meaning any attacker with network access to the device's management interface can exploit it. Given that this is an IoT/embedded device, successful exploitation could allow attackers to establish persistent access, modify device configurations, intercept network traffic, or use the compromised device as a launching point for attacks against other internal network resources.

Root Cause

The root cause of this vulnerability is insufficient input validation and sanitization in the device's web interface. User-controlled input is directly concatenated into shell commands without proper escaping or filtering of shell metacharacters. This design flaw allows attackers to break out of the intended command context and inject their own commands using common shell metacharacters such as semicolons (;), pipes (|), backticks (`), or command substitution syntax ($()).

Attack Vector

The attack is conducted over the network against the device's web management interface. An attacker can craft malicious HTTP requests containing OS command injection payloads in vulnerable parameters. Since no authentication is required, the attacker simply needs network connectivity to the target device to execute the attack.

The exploitation process typically involves:

1. Identifying a vulnerable Telesquare SDT-CW3B1 device on the network
2. Crafting an HTTP request with command injection payload in a vulnerable parameter
3. The payload bypasses input validation and is passed to a system shell function
4. Arbitrary commands execute with device privileges, typically root

For detailed technical information about the exploitation technique, refer to the Packet Storm Command Injection Report.

Detection Methods for CVE-2021-46422

Indicators of Compromise

• Unexpected outbound network connections from Telesquare SDT-CW3B1 devices to unknown IP addresses
• Unusual processes running on the device that are not part of standard firmware operations
• Modified configuration files or unauthorized changes to device settings
• Web server access logs showing requests with shell metacharacters (;, |, $(), backticks)
• Evidence of reverse shell connections or suspicious bind shells on unusual ports

Detection Strategies

• Monitor HTTP requests to Telesquare device management interfaces for common command injection patterns including shell metacharacters
• Implement network intrusion detection rules to identify exploitation attempts targeting this vulnerability
• Deploy web application firewalls (WAF) with rules to block requests containing OS command injection payloads
• Establish baseline network behavior for IoT devices and alert on anomalies such as unexpected outbound connections

Monitoring Recommendations

• Enable and regularly review access logs on the device's web management interface
• Implement network segmentation to isolate IoT devices and monitor cross-segment traffic
• Deploy endpoint detection solutions capable of monitoring embedded device behavior
• Set up alerts for any authentication bypass attempts or unusual administrative actions on network devices

How to Mitigate CVE-2021-46422

Immediate Actions Required

• Isolate affected Telesquare SDT-CW3B1 devices from untrusted networks immediately
• Restrict access to the device's web management interface using firewall rules or ACLs to trusted IP addresses only
• Disable remote management access if not required for operations
• Conduct a forensic review of potentially compromised devices to identify any indicators of exploitation
• Consider replacing vulnerable devices with alternatives that have active security support

Patch Information

At the time of this writing, no vendor patch information is available in the CVE data. Organizations should contact Telesquare directly to inquire about firmware updates that address this vulnerability. Monitor vendor communications and security advisories for updates regarding CVE-2021-46422. Additional technical details can be found in the Packet Storm security report.

Workarounds

• Implement strict network access controls to limit management interface access to trusted administrator IP addresses only
• Place vulnerable devices behind a firewall that blocks external access to the management interface
• Use VPN or jump host architecture to access device management interfaces rather than exposing them directly
• Implement network monitoring to detect and alert on exploitation attempts

# Example firewall rule to restrict management access (iptables)
# Allow management access only from trusted admin network
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