CVE-2024-2851: Tenda AC15 Firmware RCE Vulnerability

CVE-2024-2851 Overview

CVE-2024-2851 is a critical OS command injection vulnerability affecting Tenda AC15 routers running firmware versions 15.03.05.18 and 15.03.20_multi. The vulnerability exists in the formSetSambaConf function within the /goform/setsambacfg endpoint, where improper handling of the usbName parameter allows attackers to inject arbitrary operating system commands. This vulnerability can be exploited remotely without authentication, potentially allowing complete compromise of affected devices.

Critical Impact

Remote attackers can execute arbitrary OS commands on vulnerable Tenda AC15 routers without authentication, potentially leading to full device compromise, network pivoting, and persistent backdoor installation.

Affected Products

• Tenda AC15 Firmware version 15.03.05.18
• Tenda AC15 Firmware version 15.03.20_multi
• Tenda AC15 Hardware Device

Discovery Timeline

• March 24, 2024 - CVE-2024-2851 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2024-2851

Vulnerability Analysis

This vulnerability represents a classic OS command injection flaw (CWE-78) in embedded IoT firmware. The formSetSambaConf function, responsible for handling Samba configuration requests on the router's web interface, fails to properly sanitize user-supplied input in the usbName parameter before passing it to system shell commands. The attack can be initiated remotely over the network without requiring any prior authentication or user interaction, making it particularly dangerous for internet-exposed devices.

When exploited, an attacker gains the ability to execute commands with the same privileges as the web server process, which on many embedded devices runs as root. This provides complete control over the router, including the ability to modify configurations, intercept network traffic, install persistent backdoors, or use the compromised device as a pivot point for further network intrusion.

Root Cause

The root cause lies in insufficient input validation and sanitization of the usbName parameter within the formSetSambaConf function. The affected code directly incorporates user-controlled input into shell command execution without proper escaping or filtering of special characters. This allows metacharacters such as semicolons, pipes, and backticks to be interpreted as command delimiters, enabling command chaining and arbitrary command execution.

Attack Vector

The attack is conducted over the network by sending specially crafted HTTP requests to the /goform/setsambacfg endpoint on the router's web management interface. An attacker manipulates the usbName parameter to include shell metacharacters followed by malicious commands. Since no authentication is required to exploit this vulnerability, any attacker with network access to the router's management interface can trigger the command injection.

For example, an attacker could craft a request where the usbName parameter contains values like test;id; or test$(whoami) to execute additional commands. The vulnerability has been publicly disclosed and documented, increasing the risk of exploitation in the wild. For technical details on the exploitation mechanism, refer to the GitHub Vulnerability Documentation.

Detection Methods for CVE-2024-2851

Indicators of Compromise

• HTTP POST requests to /goform/setsambacfg containing shell metacharacters (;, |, $(), backticks) in the usbName parameter
• Unexpected processes spawned by the router's web server process
• Unusual outbound network connections from the router to external IP addresses
• Modifications to router configuration files or firmware
• Presence of unfamiliar files in writable directories on the router filesystem

Detection Strategies

• Implement network intrusion detection rules to monitor for suspicious HTTP requests targeting /goform/setsambacfg with command injection patterns
• Deploy web application firewall rules to block requests containing shell metacharacters in form parameters
• Monitor router system logs for unexpected command execution or error messages related to the Samba configuration handler
• Use network traffic analysis to identify anomalous connections originating from router devices

Monitoring Recommendations

• Establish baseline behavior for router management interface traffic and alert on deviations
• Configure SIEM rules to correlate web server access logs with system command execution events
• Implement periodic integrity checking of router firmware and configuration files
• Monitor for DNS queries or network connections to known malicious infrastructure from router IP addresses

How to Mitigate CVE-2024-2851

Immediate Actions Required

• Disable remote management access to the router's web interface from untrusted networks immediately
• Restrict access to the router management interface to trusted internal IP addresses only using firewall rules
• Consider placing the router management interface on a dedicated management VLAN with restricted access
• Monitor for any signs of compromise and prepare for potential device replacement if patching is not available

Patch Information

The vendor (Tenda) was contacted early about this disclosure but did not respond. As of the last update, no official patch has been released by the vendor. Organizations using affected Tenda AC15 devices should consider replacing the hardware with supported alternatives from vendors with better security response practices. For additional vulnerability tracking information, see VulDB #257775.

Workarounds

• Disable the Samba file sharing functionality on the router if not required for operations
• Place the router behind an additional firewall that can filter and inspect HTTP traffic to block malicious requests
• Implement network segmentation to limit the impact of a potentially compromised router
• Consider deploying third-party firmware (such as OpenWrt or DD-WRT if compatible) that may not contain this vulnerability

# Example: Restrict management interface access using iptables on upstream firewall
# Block external access to router management interface
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 80 -j DROP
iptables -A FORWARD -d 192.168.1.1 -p tcp --dport 443 -j DROP

# Allow management access only from trusted management workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT