CVE-2024-2813: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2813 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC15 router firmware version 15.03.20_multi. This vulnerability exists in the form_fast_setting_wifi_set function located in the /goform/fast_setting_wifi_set file. The flaw allows remote attackers to exploit improper handling of the ssid argument, leading to a stack-based buffer overflow condition that can compromise the entire device.

The exploit has been publicly disclosed, and despite early notification, the vendor (Tenda) has not responded to the disclosure. This lack of vendor engagement increases the risk profile for organizations running affected devices.

Critical Impact

Remote attackers can exploit this buffer overflow vulnerability to execute arbitrary code on the affected Tenda AC15 router, potentially gaining full control of the device without authentication.

Affected Products

• Tenda AC15 Firmware version 15.03.05.20_multi
• Tenda AC15 Hardware
• Tenda AC15 Firmware (all 15.03.20_multi variants)

Discovery Timeline

• 2024-03-22 - CVE-2024-2813 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2813

Vulnerability Analysis

This vulnerability is classified as CWE-121: Stack-based Buffer Overflow. The flaw resides in the form_fast_setting_wifi_set function, which processes WiFi configuration settings through the web management interface. When handling the ssid parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer.

The vulnerability allows unauthenticated remote attackers to send specially crafted HTTP requests to the /goform/fast_setting_wifi_set endpoint. By providing an excessively long ssid value, an attacker can overflow the stack buffer, overwrite adjacent memory including the return address, and redirect code execution to attacker-controlled shellcode.

Root Cause

The root cause of CVE-2024-2813 is insufficient input validation in the form_fast_setting_wifi_set function. The code does not perform adequate bounds checking on the ssid parameter before copying it to a stack-allocated buffer. This is a common vulnerability pattern in embedded IoT devices where memory-safe coding practices are often not enforced during firmware development.

The lack of stack protection mechanisms (such as stack canaries) in the firmware further exacerbates the exploitability of this vulnerability.

Attack Vector

The attack vector is network-based and requires no prior authentication or user interaction. An attacker with network access to the router's web management interface can exploit this vulnerability by sending a malicious HTTP POST request to the /goform/fast_setting_wifi_set endpoint.

The attack flow involves crafting an HTTP request with an oversized ssid parameter that exceeds the expected buffer size. When processed by the vulnerable function, the overflow overwrites critical stack data including saved registers and return addresses. The attacker can control the execution flow to execute arbitrary code with the privileges of the web server process, typically root on embedded devices.

For technical details on the exploitation methodology, refer to the GitHub IoT Vulnerability Documentation.

Detection Methods for CVE-2024-2813

Indicators of Compromise

• Unusual HTTP POST requests to /goform/fast_setting_wifi_set with abnormally long ssid parameters
• Unexpected router reboots or crashes following web management interface access
• Modified router configurations or unauthorized admin account creation
• Anomalous outbound network connections from the router to unknown IP addresses

Detection Strategies

• Monitor HTTP traffic to the router's web interface for requests containing oversized parameters
• Implement network-based intrusion detection rules to identify buffer overflow attack patterns targeting Tenda devices
• Deploy network segmentation to isolate IoT devices and monitor traffic crossing segment boundaries
• Use SentinelOne Singularity for network visibility to detect exploitation attempts and lateral movement from compromised devices

Monitoring Recommendations

• Enable comprehensive logging on network security appliances monitoring traffic to and from Tenda routers
• Implement alerting for any access to the /goform/fast_setting_wifi_set endpoint from untrusted networks
• Monitor for firmware modification attempts or unexpected changes to device configuration
• Review network traffic patterns for signs of command and control communication originating from router IP addresses

How to Mitigate CVE-2024-2813

Immediate Actions Required

• Restrict access to the router's web management interface to trusted networks or administrative VLANs only
• Disable remote management features if not required for operational purposes
• Implement firewall rules to block external access to port 80/443 on the affected device
• Consider replacing vulnerable Tenda AC15 routers with devices from vendors with active security response programs

Patch Information

As of the last modification date (2024-11-21), the vendor (Tenda) has not released a security patch for this vulnerability. The vendor was contacted early during the disclosure process but did not respond. Organizations should monitor VulDB #257668 for any updates regarding vendor patches.

Given the lack of vendor response, organizations are strongly encouraged to implement compensating controls and consider device replacement with supported hardware from responsive vendors.

Workarounds

• Disable the web management interface entirely and use alternative configuration methods if available
• Place the router behind a network firewall that filters and inspects HTTP traffic for malicious payloads
• Implement network access control lists (ACLs) to restrict management interface access to specific administrative IP addresses
• Use VPN connections for any remote administration requirements rather than exposing the management interface

# Example iptables rules to restrict management interface access
# Block external access to router management ports
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