CVE-2024-0924: Tenda AC10U Buffer Overflow Vulnerability

CVE-2024-0924 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC10U firmware version 15.03.06.49_multi_TDE01. The vulnerability exists within the formSetPPTPServer function, where improper handling of the startIp argument allows an attacker to trigger a stack-based buffer overflow. This vulnerability enables remote attackers to potentially execute arbitrary code or cause a denial of service condition without requiring any authentication or user interaction.

Critical Impact

This vulnerability allows unauthenticated remote attackers to exploit the buffer overflow in the PPTP server configuration function, potentially leading to complete device compromise, arbitrary code execution, or denial of service.

Affected Products

• Tenda AC10U Firmware version 15.03.06.49_multi_TDE01
• Tenda AC10U hardware devices running affected firmware
• Network environments utilizing Tenda AC10U routers with PPTP server functionality

Discovery Timeline

• 2024-01-26 - CVE-2024-0924 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-0924

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-121), one of the most dangerous memory corruption vulnerabilities in embedded systems. The flaw resides in the formSetPPTPServer function, which handles PPTP (Point-to-Point Tunneling Protocol) server configuration on the Tenda AC10U router.

When processing the startIp parameter, the function fails to properly validate the length of user-supplied input before copying it to a fixed-size stack buffer. This allows an attacker to supply an oversized value that overwrites adjacent memory on the stack, including the return address and other critical control data.

The vulnerability can be exploited remotely over the network without requiring any authentication or user interaction, making it particularly dangerous for exposed devices. Successful exploitation could allow attackers to execute arbitrary code with the privileges of the router's web service, potentially leading to complete device compromise.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formSetPPTPServer function. The function accepts the startIp parameter from user input without properly verifying its length before copying it to a stack-allocated buffer. This classic buffer overflow pattern is common in embedded device firmware where memory-safe programming practices may not be consistently applied.

The lack of bounds checking allows attackers to supply input that exceeds the expected buffer size, causing data to overflow into adjacent stack memory and corrupt the program's execution flow.

Attack Vector

The attack vector for CVE-2024-0924 is network-based, meaning an attacker can exploit this vulnerability remotely. The attack requires no authentication and no user interaction, making it a direct attack path against vulnerable devices.

An attacker would craft a malicious HTTP request to the router's web interface targeting the PPTP server configuration endpoint. By manipulating the startIp parameter with an oversized payload containing shellcode or ROP gadgets, the attacker can hijack the execution flow and achieve arbitrary code execution.

The exploitation technique involves overwriting the saved return address on the stack with a controlled value, redirecting execution to attacker-supplied code when the function returns. For detailed technical analysis, refer to the GitHub IoT Configuration Guide and the VulDB advisory #252129.

Detection Methods for CVE-2024-0924

Indicators of Compromise

• Unexpected crashes or reboots of the Tenda AC10U router, particularly when accessing PPTP configuration
• Abnormally large HTTP POST requests targeting the router's management interface with oversized startIp parameters
• Unusual network traffic originating from the router indicating potential command-and-control communication
• Modification of router configuration or firmware without administrator action

Detection Strategies

• Monitor HTTP traffic to the router's web management interface for requests containing abnormally long startIp parameter values
• Implement network intrusion detection rules to identify buffer overflow exploit patterns targeting Tenda devices
• Review router access logs for suspicious POST requests to PPTP server configuration endpoints
• Deploy network segmentation to isolate IoT devices and monitor for anomalous outbound connections

Monitoring Recommendations

• Enable logging on network firewalls and IDS/IPS systems to capture traffic to and from Tenda AC10U devices
• Establish baseline network behavior for router devices and alert on deviations indicating potential compromise
• Monitor for known exploit signatures associated with Tenda router vulnerabilities in network traffic
• Regularly audit device configurations to detect unauthorized changes that may indicate exploitation

How to Mitigate CVE-2024-0924

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote management access if not required for operations
• Place vulnerable Tenda AC10U devices behind a firewall that blocks untrusted external access
• Consider replacing affected devices with alternatives if the vendor does not provide a security patch

Patch Information

No official patch has been released by Tenda for this vulnerability. According to the vulnerability disclosure, the vendor was contacted early about this issue but did not respond. Users should monitor Tenda's official channels for any future firmware updates and apply them immediately when available.

Workarounds

• Disable the PPTP server functionality if not required for your network environment
• Implement strict network access controls to limit who can reach the router's management interface
• Use a VPN or jump host to access the router's administration panel rather than exposing it directly
• Consider network segmentation to isolate the vulnerable device from critical network assets

# Configuration example - Restrict management interface access via firewall
# Block external access to Tenda router management port (typically port 80/443)
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