CVE-2024-2809: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2809 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda AC15 router firmware. The vulnerability exists in the formSetFirewallCfg function within the /goform/SetFirewallCfg endpoint. Improper handling of the firewallEn argument allows remote attackers to overflow the stack buffer, potentially leading to remote code execution or denial of service. The exploit has been publicly disclosed, and the vendor did not respond to early disclosure attempts.

Critical Impact
Remote attackers can exploit this stack-based buffer overflow without authentication to potentially execute arbitrary code or crash the device, compromising network security at the router level.

Affected Products

Tenda AC15 Firmware version 15.03.05.18
Tenda AC15 Firmware version 15.03.20_multi
Tenda AC15 Hardware version 1.0

Discovery Timeline

2024-03-22 - CVE-2024-2809 published to NVD
2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2809

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when user-controlled input exceeds the bounds of a stack-allocated buffer. In the case of CVE-2024-2809, the formSetFirewallCfg function in the Tenda AC15 firmware fails to properly validate the length of the firewallEn argument before copying it to a fixed-size buffer on the stack.

The network-accessible attack vector means that any attacker with network access to the router's web interface can potentially exploit this vulnerability. No authentication is required, and no user interaction is needed, making this a highly exploitable flaw. Successful exploitation can result in complete compromise of confidentiality, integrity, and availability of the affected device.

Root Cause

The root cause of this vulnerability lies in inadequate input validation within the formSetFirewallCfg function. When processing HTTP POST requests to /goform/SetFirewallCfg, the firmware copies the firewallEn parameter value directly into a stack buffer without verifying that the input length does not exceed the buffer's allocated size. This classic buffer overflow pattern allows attackers to overwrite adjacent stack memory, including return addresses, enabling control flow hijacking.

Attack Vector

The attack can be conducted remotely over the network by sending a specially crafted HTTP POST request to the vulnerable endpoint /goform/SetFirewallCfg. An attacker would submit an oversized value for the firewallEn parameter, overflowing the stack buffer. By carefully crafting the overflow payload, an attacker can overwrite the function's return address and redirect execution to malicious shellcode, potentially gaining full control over the router.

The vulnerability is particularly dangerous on IoT devices like routers because:

They often run with elevated privileges
They serve as network gateway devices with access to all traffic
Firmware updates may be infrequent or unavailable
Exploitation can enable persistent backdoor access to the network

For detailed technical analysis, see the GitHub vulnerability documentation and the VulDB entry #257664.

Detection Methods for CVE-2024-2809

Indicators of Compromise

Unexpected device reboots or crashes of the Tenda AC15 router
Unusual network traffic patterns originating from or directed to the router's management interface
HTTP POST requests to /goform/SetFirewallCfg with abnormally large firewallEn parameter values
Signs of unauthorized configuration changes or firmware modifications

Detection Strategies

Implement network monitoring to detect HTTP POST requests targeting /goform/SetFirewallCfg with oversized payloads
Deploy intrusion detection/prevention systems (IDS/IPS) with rules to identify buffer overflow exploitation attempts against Tenda devices
Monitor for anomalous behavior from router devices including unexpected outbound connections or process spawning
Analyze network traffic logs for exploitation patterns matching known Tenda AC15 attack signatures

Monitoring Recommendations

Enable logging on network perimeter devices to capture traffic to and from Tenda router management interfaces
Implement network segmentation to isolate IoT and router management interfaces from general network traffic
Configure alerting for any unexpected access attempts to router configuration endpoints
Regularly audit router configurations and firmware versions to ensure compliance with security baselines

How to Mitigate CVE-2024-2809

Immediate Actions Required

Restrict access to the router's web management interface to trusted IP addresses only
Place the router management interface on a separate, isolated network segment
Implement firewall rules to block external access to /goform/SetFirewallCfg and other sensitive endpoints
Consider replacing affected Tenda AC15 devices with alternative hardware from vendors with better security response practices
Monitor network traffic for exploitation attempts while awaiting a vendor patch

Patch Information

No official patch has been released by Tenda. The vendor was contacted about this disclosure but did not respond. Users should consider replacing affected devices or implementing strict network access controls to mitigate risk. Monitor the VulDB entry for updates on vendor response or patch availability.

Workarounds

Disable remote management access to the router's web interface if not required
Implement access control lists (ACLs) to limit management interface access to specific trusted hosts
Deploy a web application firewall (WAF) or reverse proxy in front of the management interface to filter malicious requests
Use VPN-only access for router administration to prevent direct exposure of the management interface

bash

# Example: Restrict management interface access via iptables on upstream device
# Block external access to the Tenda AC15 management 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 management access only from trusted admin workstation
iptables -I FORWARD -s 192.168.1.100 -d 192.168.1.1 -p tcp --dport 80 -j ACCEPT