CVE-2024-2807: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2807 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda AC15 wireless router firmware. This vulnerability exists within the formExpandDlnaFile function located in the /goform/expandDlnaFile endpoint. When the filePath argument is manipulated with excessive input data, it triggers a stack-based buffer overflow condition that can be exploited remotely without authentication.

The vulnerability allows remote attackers to potentially execute arbitrary code, crash the device, or gain complete control over the affected router. Since the Tenda AC15 is a consumer-grade wireless router commonly deployed in home and small business environments, successful exploitation could lead to network compromise, data interception, or use of the device in botnet attacks.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to execute arbitrary code or cause denial of service on Tenda AC15 routers without any authentication requirements.

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-2024-2807 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2807

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-121), which occurs when data is written beyond the boundaries of a fixed-length stack buffer. In the context of the Tenda AC15 router, the formExpandDlnaFile function fails to properly validate the length of input received through the filePath parameter before copying it to a stack-allocated buffer.

Stack-based buffer overflows are particularly dangerous in embedded devices like routers because they often lack modern memory protection mechanisms such as ASLR (Address Space Layout Randomization) or stack canaries. This makes exploitation more reliable and increases the severity of the vulnerability.

The attack can be initiated remotely over the network, requiring no authentication or user interaction. This makes the vulnerability highly accessible to attackers who can reach the device's web management interface.

Root Cause

The root cause of this vulnerability is improper input validation in the formExpandDlnaFile function. The function accepts user-supplied input through the filePath argument without verifying that the input length does not exceed the size of the destination stack buffer. When an attacker provides an overly long string, the function copies this data past the buffer boundaries, overwriting adjacent stack memory including return addresses and saved registers.

This type of vulnerability commonly occurs in embedded device firmware written in C/C++ where manual memory management is required and bounds checking is not enforced by the language runtime.

Attack Vector

The attack is executed by sending a crafted HTTP request to the /goform/expandDlnaFile endpoint on the router's web management interface. The attacker manipulates the filePath parameter with a payload designed to overflow the stack buffer.

The attack requires network access to the router's management interface. In default configurations, this interface may be accessible from the local network. If remote management is enabled, the attack surface extends to the internet.

The vulnerability allows an attacker to overwrite the function's return address on the stack, potentially redirecting execution to attacker-controlled code. This can lead to complete device compromise, including the ability to modify firmware, intercept network traffic, or use the device as a pivot point for further attacks.

Technical details and proof-of-concept information have been documented in the GitHub IoT Vulnerability Documentation.

Detection Methods for CVE-2024-2807

Indicators of Compromise

• Unexpected HTTP POST requests to /goform/expandDlnaFile with unusually long filePath parameters
• Router crashes, reboots, or unresponsive behavior without clear cause
• Unauthorized configuration changes or new administrative accounts on the router
• Anomalous outbound network traffic from the router to unknown IP addresses
• Modified firmware or unexpected processes running on the device

Detection Strategies

• Implement network intrusion detection rules to flag requests to /goform/expandDlnaFile containing filePath values exceeding normal length thresholds
• Monitor HTTP traffic to the router's management interface for patterns consistent with buffer overflow exploitation attempts
• Deploy endpoint detection on network segments to identify potential lateral movement following router compromise
• Review router logs for failed authentication attempts or unusual access patterns to the web interface

Monitoring Recommendations

• Enable logging on the router if supported and forward logs to a centralized SIEM for analysis
• Implement network segmentation to isolate IoT and networking devices from critical systems
• Conduct regular firmware version audits to identify devices running vulnerable versions
• Monitor for DNS queries or network connections to known malicious infrastructure originating from router IP addresses

How to Mitigate CVE-2024-2807

Immediate Actions Required

• Disable remote management access to the router's web interface immediately
• Restrict access to the router's management interface to trusted IP addresses or network segments only
• Place the router behind a firewall that can inspect and filter malicious requests
• Consider replacing vulnerable devices with alternative hardware if no patch is available
• Monitor network traffic for exploitation attempts while waiting for vendor remediation

Patch Information

At the time of disclosure, the vendor (Tenda) was contacted but did not respond. No official security patch has been released for this vulnerability. Users should check the Tenda support website periodically for firmware updates and monitor security advisories.

Given the lack of vendor response, organizations with critical security requirements should consider migrating to alternative router solutions that have active security support and vulnerability management programs.

Workarounds

• Disable the web management interface entirely if remote configuration is not required
• Implement network-level access controls using a firewall to restrict access to the management interface (port 80/443) to specific administrator IP addresses
• Deploy a web application firewall (WAF) in front of the management interface to filter requests with oversized parameters
• Segment the network to ensure the router's management interface is not accessible from untrusted network zones
• Consider using a VPN to access the management interface rather than exposing it directly

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

# Allow management access only from specific admin IP
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s <admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s <admin_ip> -j ACCEPT

# Block all other access to management ports
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP