CVE-2024-2808: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2808 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC15 router firmware versions 15.03.05.18 and 15.03.20_multi. This vulnerability exists in the formQuickIndex function within the /goform/QuickIndex file and can be exploited through manipulation of the PPPOEPassword argument. The vulnerability allows remote attackers to potentially execute arbitrary code on affected devices without requiring authentication.

Critical Impact

This stack-based buffer overflow vulnerability enables remote attackers to compromise Tenda AC15 routers via network access, potentially leading to complete device takeover, network traffic interception, and use of the compromised device as a pivot point for further network attacks.

Affected Products

• Tenda AC15 Firmware version 15.03.05.18
• Tenda AC15 Firmware version 15.03.05.20_multi
• Tenda AC15 Hardware version 1.0

Discovery Timeline

• 2024-03-22 - CVE-2024-2808 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2808

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw that occurs when the formQuickIndex function fails to properly validate the length of user-supplied input in the PPPOEPassword parameter. When an attacker supplies an oversized value for this parameter, the function writes data beyond the allocated stack buffer boundaries, corrupting adjacent memory and potentially overwriting critical control data such as return addresses.

The exploit has been publicly disclosed and documented, indicating that technical details are readily available to potential attackers. The vendor (Tenda) was contacted regarding this vulnerability but did not respond, leaving affected devices without an official patch.

Root Cause

The root cause of this vulnerability is improper input validation in the formQuickIndex function. The function accepts the PPPOEPassword argument from user input via the /goform/QuickIndex endpoint without performing adequate bounds checking. When processing this parameter, the function copies the user-supplied data into a fixed-size stack buffer without verifying that the input length does not exceed the buffer's capacity, resulting in a classic stack-based buffer overflow condition.

Attack Vector

This vulnerability can be exploited remotely over the network without requiring authentication or user interaction. An attacker can send a specially crafted HTTP request to the /goform/QuickIndex endpoint on a vulnerable Tenda AC15 router, including an overly long PPPOEPassword parameter value. This malicious input overwrites the stack buffer and potentially corrupts control flow data, enabling the attacker to redirect execution to attacker-controlled code.

The attack can be performed from anywhere on the network that can reach the router's web management interface, making this particularly dangerous if the management interface is exposed to the internet or if an attacker has already gained access to the local network.

For detailed technical analysis and proof-of-concept information, refer to the GitHub IoT Vulnerability Documentation and the VulDB advisory.

Detection Methods for CVE-2024-2808

Indicators of Compromise

• Unusual HTTP POST requests to /goform/QuickIndex with abnormally large PPPOEPassword parameter values
• Router crashes or unexpected reboots potentially indicative of exploitation attempts
• Unauthorized configuration changes on the router
• Anomalous outbound network traffic from the router suggesting command-and-control communication

Detection Strategies

• Monitor web server logs on Tenda AC15 routers for requests to /goform/QuickIndex with oversized parameter values
• Implement network-based intrusion detection rules to identify HTTP requests containing excessively long PPPOEPassword fields
• Deploy network traffic analysis to detect patterns consistent with buffer overflow exploitation attempts targeting embedded devices
• Establish behavioral baselines for router activity and alert on deviations that may indicate compromise

Monitoring Recommendations

• Configure SIEM solutions to alert on suspicious activity patterns targeting IoT and network devices
• Monitor for firmware integrity changes or unauthorized modifications to router configuration
• Implement network segmentation to isolate management interfaces from untrusted networks
• Regularly audit network device configurations and compare against known-good baselines

How to Mitigate CVE-2024-2808

Immediate Actions Required

• Restrict access to the Tenda AC15 router's web management interface to trusted IP addresses only
• Disable remote management access from the WAN/internet if enabled
• Place the router behind a firewall that can filter malicious requests to /goform/QuickIndex
• Consider replacing affected Tenda AC15 devices with alternative routers from vendors with better security response practices

Patch Information

No official patch is currently available from Tenda. The vendor was contacted regarding this vulnerability but did not respond. Users should implement the recommended workarounds and monitor for any future firmware updates from Tenda that may address this issue.

For additional details, consult the VulDB advisory #257663.

Workarounds

• Implement access control lists (ACLs) to restrict access to the router's management interface to trusted internal IP addresses only
• Use a web application firewall (WAF) or intrusion prevention system (IPS) to block requests with oversized parameter values targeting /goform/QuickIndex
• Disable the web management interface entirely if not required for ongoing administration
• Consider network segmentation to isolate vulnerable IoT devices from critical network assets

# Example: Block external access to router management (firewall rule concept)
# Apply appropriate firewall rules on your perimeter firewall to block
# inbound access to the router's web management port (typically TCP/80 or TCP/443)

# If using iptables on a Linux-based firewall:
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP

# Allow management only from trusted admin workstation
iptables -A FORWARD -s <admin_ip> -d <router_ip> -p tcp --dport 80 -j ACCEPT