CVE-2024-0922: Tenda AC10U Buffer Overflow Vulnerability

CVE-2024-0922 Overview

A critical stack-based buffer overflow vulnerability has been identified in the Tenda AC10U router firmware version 15.03.06.49_multi_TDE01. The vulnerability exists within the formQuickIndex function, where improper handling of the PPPOEPassword argument allows an attacker to trigger a buffer overflow condition. This flaw can be exploited remotely without authentication, potentially allowing attackers to execute arbitrary code or cause a denial of service on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to gain complete control over affected Tenda AC10U routers, potentially compromising the entire network segment behind the device.

Affected Products

• Tenda AC10U Firmware version 15.03.06.49_multi_TDE01
• Tenda AC10U Hardware version 1.0

Discovery Timeline

• 2024-01-26 - CVE-2024-0922 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-0922

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a dangerous memory corruption issue that occurs when a program writes data beyond the bounds of a fixed-size buffer allocated on the stack. In the context of the Tenda AC10U router, the vulnerable formQuickIndex function fails to properly validate the length of user-supplied input provided through the PPPOEPassword parameter.

When an attacker supplies an oversized value for the PPPOEPassword argument, the function attempts to copy this data into a stack-allocated buffer without adequate bounds checking. This allows the attacker to overwrite adjacent memory on the stack, including critical control data such as return addresses and saved frame pointers. By carefully crafting the overflow payload, an attacker can redirect program execution to arbitrary code.

Root Cause

The root cause of this vulnerability lies in the unsafe handling of user-supplied input within the formQuickIndex function. The firmware developers failed to implement proper input length validation before copying the PPPOEPassword parameter into a fixed-size stack buffer. This is a common vulnerability pattern in embedded systems where legacy C functions like strcpy() or sprintf() are used without length checks.

Attack Vector

The vulnerability is exploitable remotely over the network. An unauthenticated attacker can send a specially crafted HTTP request to the router's web management interface containing a malicious PPPOEPassword value. The attack requires no user interaction and can be executed with low complexity. Upon successful exploitation, the attacker can achieve full compromise of the router, including the ability to execute arbitrary commands, intercept network traffic, or pivot to other devices on the network.

The exploit methodology involves sending a crafted request to the formQuickIndex endpoint with an oversized PPPOEPassword parameter. The overflow overwrites the return address on the stack, allowing the attacker to redirect execution to shellcode embedded within the payload or to existing code gadgets within the firmware. Technical details of this vulnerability have been publicly disclosed through the GitHub IoT Documentation.

Detection Methods for CVE-2024-0922

Indicators of Compromise

• Unexpected HTTP requests to the router's web interface containing abnormally long PPPOEPassword parameters
• Router crashes, reboots, or unresponsive behavior following network requests
• Unusual outbound connections from the router to unknown external IP addresses
• Modified router configuration or unauthorized administrative accounts

Detection Strategies

• Monitor web server logs on the router for requests to the formQuickIndex endpoint with unusually large parameter values
• Implement network intrusion detection rules to identify buffer overflow attack patterns targeting Tenda routers
• Deploy network segmentation to isolate router management interfaces from untrusted networks
• Use firmware integrity verification tools to detect unauthorized modifications to the router's flash memory

Monitoring Recommendations

• Enable logging on the router's management interface and forward logs to a centralized SIEM for analysis
• Monitor for anomalous network traffic patterns originating from or destined to the router
• Implement alerts for multiple failed authentication attempts or configuration changes on the device
• Conduct periodic firmware integrity checks to ensure the device has not been compromised

How to Mitigate CVE-2024-0922

Immediate Actions Required

• Restrict access to the router's web management interface to trusted IP addresses only
• Disable remote management features if not required for operations
• Place the router behind an additional firewall or network segmentation to limit exposure
• Monitor the vendor's support channels for firmware updates addressing this vulnerability

Patch Information

At the time of this writing, the vendor (Tenda) was contacted regarding this vulnerability but did not respond. No official patch is currently available. Users are advised to implement the workarounds listed below and monitor for future firmware updates. For additional vulnerability details, refer to VulDB #252127.

Workarounds

• Disable the web-based management interface entirely if not required
• Use firewall rules to restrict access to the router's management ports (typically TCP 80/443)
• Consider replacing the affected device with a router from a vendor with better security response practices
• If remote management is required, use a VPN to secure access rather than exposing the interface directly

# 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