CVE-2024-2811: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2811 Overview

A critical stack-based buffer overflow vulnerability has been discovered in the Tenda AC15 wireless router firmware version 15.03.20_multi. The vulnerability exists in the formWifiWpsStart function located in the /goform/WifiWpsStart endpoint. Improper handling of the index argument allows attackers to overflow a stack buffer, potentially leading to remote code execution on the affected device.

This vulnerability is particularly concerning as it can be exploited remotely without authentication, putting home and small business networks at significant risk. The vendor (Tenda) was contacted about this disclosure but did not respond, leaving affected devices potentially unpatched.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to execute arbitrary code on Tenda AC15 routers, potentially gaining full control of the network device without authentication.

Affected Products

• Tenda AC15 Firmware version 15.03.05.20_multi
• Tenda AC15 Hardware

Discovery Timeline

• 2024-03-22 - CVE-2024-2811 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2811

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), affecting the formWifiWpsStart function in the Tenda AC15 router firmware. The function processes user-supplied input through the index parameter without proper bounds checking, allowing an attacker to write beyond the allocated stack buffer.

Stack-based buffer overflows in embedded devices like routers are particularly dangerous because these devices often lack modern memory protections such as ASLR (Address Space Layout Randomization) or stack canaries. This makes exploitation more reliable and increases the likelihood of successful remote code execution.

The vulnerability is accessible via network without requiring any authentication or user interaction, making it an attractive target for automated attacks and botnet recruitment campaigns targeting IoT devices.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the formWifiWpsStart function. When processing the index argument received from HTTP requests to /goform/WifiWpsStart, the firmware fails to verify that the input length does not exceed the size of the destination buffer on the stack. This allows attackers to supply oversized input that overwrites adjacent stack memory, including the return address, enabling control flow hijacking.

Attack Vector

The attack can be launched remotely via network access to the router's web management interface. An attacker sends a specially crafted HTTP request to the /goform/WifiWpsStart endpoint with a malicious index parameter value designed to overflow the stack buffer. Since no authentication is required to reach this endpoint, any attacker with network access to the router (including from the WAN interface if exposed) can attempt exploitation.

The attack flow typically involves:

1. Crafting an HTTP request with an oversized index parameter
2. Sending the request to the vulnerable /goform/WifiWpsStart endpoint
3. Overwriting the stack return address with attacker-controlled values
4. Redirecting execution to shellcode or ROP gadgets for code execution

Technical details and proof-of-concept information are available in the GitHub IoT Vulnerability Document.

Detection Methods for CVE-2024-2811

Indicators of Compromise

• Unusual HTTP requests to /goform/WifiWpsStart with abnormally large index parameter values
• Router crashes, reboots, or instability potentially indicating exploitation attempts
• Unexpected outbound network connections from the router to unknown IP addresses
• Modified router configuration or firmware without administrator action

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests containing oversized parameters to /goform/WifiWpsStart
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Review router logs for repeated access attempts to the vulnerable endpoint
• Deploy network segmentation to isolate IoT devices and enable better traffic monitoring

Monitoring Recommendations

• Enable logging on network firewalls to capture traffic to and from Tenda AC15 devices
• Implement anomaly detection for router behavior including unexpected reboots or configuration changes
• Monitor for firmware integrity by periodically checking device configurations
• Use network traffic analysis tools to identify potential command and control communications from compromised devices

How to Mitigate CVE-2024-2811

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if enabled on the WAN interface
• Implement network segmentation to isolate the vulnerable router from critical systems
• Consider replacing the affected device with a router from a vendor that provides active security support

Patch Information

No patch is currently available from Tenda. The vendor was contacted about this disclosure but did not respond. Users should monitor Tenda's official website for potential firmware updates, though given the vendor's non-response, a patch may not be forthcoming.

For additional technical information, refer to:

• VulDB Entry #257666
• VulDB CTI Information

Workarounds

• Block external access to the router's management interface using firewall rules
• Disable WPS functionality if possible through router settings
• Place the router behind an additional firewall or security device
• Limit access to the /goform/ endpoint path through network access controls
• Consider deploying a more secure alternative router if continued use poses unacceptable risk

# Example iptables rules to restrict access to router management interface
# Apply on upstream firewall or security device

# Block external access to router web interface (adjust IP as needed)
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 only specific trusted management IPs
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT