CVE-2024-2856: Tenda AC10 Buffer Overflow Vulnerability

CVE-2024-2856 Overview

A critical stack-based buffer overflow vulnerability has been identified in Tenda AC10 routers running firmware versions 16.03.10.13 and 16.03.10.20. The vulnerability exists in the fromSetSysTime function within the /goform/SetSysTimeCfg endpoint, where improper handling of the timeZone argument allows remote attackers to overflow a stack-based buffer. This vulnerability can be exploited remotely without authentication, potentially allowing attackers to execute arbitrary code or cause a denial of service condition on affected devices.

Critical Impact

Remote attackers can exploit this vulnerability to gain complete control over affected Tenda AC10 routers without authentication, potentially compromising the entire network segment.

Affected Products

• Tenda AC10 Firmware version 16.03.10.13
• Tenda AC10 Firmware version 16.03.10.20
• Tenda AC10 Hardware version 4.0

Discovery Timeline

• 2024-03-24 - CVE-2024-2856 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2024-2856

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), affecting the system time configuration functionality of Tenda AC10 routers. The fromSetSysTime function processes user-supplied input from the timeZone parameter without adequate bounds checking. When an attacker sends a specially crafted HTTP request to the /goform/SetSysTimeCfg endpoint with an oversized timeZone value, the input overflows the fixed-size stack buffer allocated for this parameter.

The lack of input validation allows attackers to corrupt adjacent stack memory, potentially overwriting the function's return address. This enables control flow hijacking, where the attacker can redirect execution to arbitrary memory locations or injected shellcode.

Root Cause

The root cause of this vulnerability is insufficient input validation and the absence of proper bounds checking when copying the timeZone parameter into a fixed-size stack buffer within the fromSetSysTime function. The firmware fails to verify that the length of user-supplied input does not exceed the allocated buffer size before performing the copy operation. This classic programming error in embedded firmware development allows stack-based buffer overflow conditions to occur.

Attack Vector

The attack can be launched remotely over the network by sending a malicious HTTP POST request to the vulnerable endpoint /goform/SetSysTimeCfg. The attacker manipulates the timeZone argument with a payload exceeding the expected buffer size. Since no authentication is required to access this endpoint, any network-adjacent attacker can exploit this vulnerability. The attack requires no user interaction and can be automated for mass exploitation of vulnerable devices.

The vulnerability exploitation typically involves:

1. Sending an HTTP POST request to the /goform/SetSysTimeCfg endpoint
2. Including an oversized timeZone parameter value designed to overflow the stack buffer
3. Carefully crafting the overflow payload to overwrite the return address with attacker-controlled values
4. Achieving code execution or denial of service on the target device

For detailed technical analysis of the vulnerability, see the GitHub IoT Vulnerability Document.

Detection Methods for CVE-2024-2856

Indicators of Compromise

• Unusual HTTP POST requests targeting /goform/SetSysTimeCfg with abnormally large timeZone parameter values
• Router instability, unexpected reboots, or unresponsive web interfaces indicating potential exploitation attempts
• Unexpected network traffic originating from the router to external command and control servers
• Modified router configuration or firmware settings not authorized by administrators

Detection Strategies

• Implement network intrusion detection rules to identify HTTP POST requests to /goform/SetSysTimeCfg containing oversized payloads
• Monitor router logs for repeated failed requests or crashes associated with system time configuration changes
• Deploy application-layer firewalls that can inspect HTTP payload sizes and flag anomalous parameter lengths
• Use vulnerability scanners to identify Tenda AC10 devices running affected firmware versions 16.03.10.13 or 16.03.10.20

Monitoring Recommendations

• Establish baseline network behavior for IoT devices and alert on deviations from normal communication patterns
• Configure SNMP or syslog monitoring on network devices to capture router crash events or unexpected service restarts
• Implement network segmentation monitoring to detect lateral movement attempts from compromised IoT devices
• Schedule regular firmware version audits across all Tenda router deployments

How to Mitigate CVE-2024-2856

Immediate Actions Required

• Identify and inventory all Tenda AC10 devices running firmware versions 16.03.10.13 or 16.03.10.20 in your network
• Isolate affected devices from critical network segments until patches are applied or devices are replaced
• Disable remote administration and external access to the router management interface
• Implement network access controls to restrict access to the router's web interface to trusted IP addresses only
• Consider replacing affected devices with alternative router hardware if vendor patches are not available

Patch Information

At the time of disclosure, the vendor (Tenda) was contacted but did not respond. No official patch has been released by the vendor. Organizations should monitor Tenda's official support channels for any future firmware updates addressing this vulnerability. Given the vendor's non-response, organizations may need to consider device replacement with supported alternatives. Additional information is available through the VulDB Record #257780.

Workarounds

• Restrict network access to the /goform/SetSysTimeCfg endpoint using firewall rules or router access control lists
• Disable the web management interface entirely and manage devices through serial console if physical access is available
• Place affected routers behind a VPN or secure gateway to limit exposure to potential attackers
• Implement network segmentation to isolate IoT devices from critical infrastructure

# Example iptables rule to block access to vulnerable endpoint (apply on upstream firewall)
iptables -A FORWARD -p tcp --dport 80 -d <ROUTER_IP> -m string --string "/goform/SetSysTimeCfg" --algo bm -j DROP

# Restrict management interface access to specific admin IP
iptables -A FORWARD -p tcp --dport 80 -d <ROUTER_IP> -s ! <ADMIN_IP> -j DROP