CVE-2024-2855: Tenda AC15 Buffer Overflow Vulnerability

CVE-2024-2855 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC15 wireless routers. The vulnerability exists in the fromSetSysTime function within the /goform/SetSysTimeCfg endpoint. Improper handling of the time argument allows remote attackers to trigger a stack-based buffer overflow, potentially leading to arbitrary code execution or denial of service. The exploit has been publicly disclosed, and the vendor was contacted but did not respond to the disclosure.

Critical Impact

Remote attackers can exploit this vulnerability without authentication to potentially execute arbitrary code or crash affected Tenda AC15 routers, compromising network security and availability.

Affected Products

• Tenda AC15 Firmware version 15.03.05.18
• Tenda AC15 Firmware version 15.03.05.19
• Tenda AC15 Firmware version 15.03.20_multi

Discovery Timeline

• 2024-03-24 - CVE-2024-2855 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2855

Vulnerability Analysis

This vulnerability is a stack-based buffer overflow (CWE-121) affecting the Tenda AC15 router firmware. The flaw resides in the fromSetSysTime function, which processes system time configuration requests sent to the /goform/SetSysTimeCfg endpoint. When the function receives a maliciously crafted time argument, it fails to properly validate the input length before copying data to a fixed-size stack buffer. This allows an attacker to overwrite adjacent stack memory, including the return address, potentially hijacking program execution flow.

The vulnerability can be exploited remotely over the network without requiring any authentication or user interaction, making it particularly dangerous for consumer and small business networks where these routers are commonly deployed. A successful exploit could result in complete device compromise, allowing attackers to intercept network traffic, pivot to other devices on the network, or render the router inoperable.

Root Cause

The root cause of this vulnerability is insufficient input validation in the fromSetSysTime function. The function does not properly check the length of the time parameter before copying it into a stack-allocated buffer. This classic buffer overflow pattern allows attackers to supply oversized input that exceeds the buffer boundaries, corrupting adjacent memory on the stack. The lack of proper bounds checking is a common issue in embedded device firmware where memory-safe programming practices may not be consistently applied.

Attack Vector

The attack vector is network-based, targeting the router's web management interface. An attacker can craft a malicious HTTP POST request to the /goform/SetSysTimeCfg endpoint with an oversized time parameter. Since no authentication is required to exploit this vulnerability, any attacker with network access to the router's management interface can attempt exploitation. The attack does not require user interaction and can be automated for mass exploitation of vulnerable devices.

The vulnerability can be exploited by sending a specially crafted HTTP request containing an oversized payload in the time parameter to the /goform/SetSysTimeCfg endpoint. For detailed technical analysis and proof of concept, refer to the GitHub Vulnerability Documentation.

Detection Methods for CVE-2024-2855

Indicators of Compromise

• Unexpected router reboots or crashes, particularly after receiving HTTP requests to the management interface
• Anomalous HTTP POST requests to /goform/SetSysTimeCfg with unusually large time parameter values
• Unusual outbound network connections originating from the router device
• Modified router configuration or firmware without administrator action

Detection Strategies

• Monitor network traffic for HTTP POST requests to /goform/SetSysTimeCfg containing abnormally large payloads
• Implement network intrusion detection rules to identify buffer overflow exploitation patterns targeting Tenda devices
• Deploy SentinelOne Singularity for network monitoring to detect exploitation attempts and lateral movement from compromised IoT devices

Monitoring Recommendations

• Enable logging on the router management interface if supported by the firmware
• Monitor for unexpected access to the router's administrative endpoints from unauthorized IP addresses
• Implement network segmentation to isolate IoT devices and limit the impact of potential compromise
• Use SentinelOne's network discovery capabilities to maintain visibility into vulnerable devices on your network

How to Mitigate CVE-2024-2855

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 a firewall that can filter malicious requests to the management interface
• Consider replacing vulnerable Tenda AC15 devices with alternative networking equipment from vendors with responsive security practices

Patch Information

At the time of disclosure, Tenda was contacted but did not respond to the vulnerability report. No official patch is currently available from the vendor. Organizations using affected devices should implement the workarounds listed below and consider device replacement as a long-term solution. Monitor VulDB for any updates regarding vendor response or patch availability.

Workarounds

• Disable WAN access to the router's management interface to prevent remote exploitation
• Implement strict firewall rules to block external access to port 80/443 on the router
• Use VPN for remote administration instead of exposing the management interface directly
• Enable MAC address filtering on the LAN to limit which devices can access the management interface

# Example iptables rules to restrict access to router management (apply on upstream firewall)
# Block external access to router management interface
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 only trusted admin IP to access management
iptables -I FORWARD -s <TRUSTED_ADMIN_IP> -d <ROUTER_IP> -p tcp --dport 80 -j ACCEPT