CVE-2026-2192: Tenda AC9 Buffer Overflow Vulnerability

CVE-2026-2192 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda AC9 routers running firmware version 15.03.06.42_multi. The vulnerability exists in the formGetRebootTimer function, which improperly handles the sys.schedulereboot.start_time and sys.schedulereboot.end_time arguments. An authenticated attacker with administrative privileges can remotely exploit this vulnerability to trigger a buffer overflow condition, potentially leading to arbitrary code execution or denial of service on the affected device.

Critical Impact

This network-accessible vulnerability allows authenticated attackers to execute arbitrary code or crash the device by exploiting buffer overflow conditions in the router's reboot timer functionality. The exploit has been publicly disclosed.

Affected Products

• Tenda AC9 Firmware version 15.03.06.42_multi
• Tenda AC9 Hardware

Discovery Timeline

• February 8, 2026 - CVE-2026-2192 published to NVD
• February 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-2192

Vulnerability Analysis

This vulnerability is classified as a stack-based buffer overflow (CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer). The flaw resides in the formGetRebootTimer function within the Tenda AC9 firmware, which processes scheduled reboot timer parameters without adequate bounds checking.

When processing the sys.schedulereboot.start_time and sys.schedulereboot.end_time arguments, the function fails to validate the length of user-supplied input before copying it into a fixed-size stack buffer. This allows an attacker to supply oversized input that overwrites adjacent stack memory, including the return address, potentially redirecting program execution to attacker-controlled code.

The vulnerability requires network access and high-level privileges (administrative authentication) to exploit. However, once authenticated, the attacker can reliably trigger the overflow condition to achieve code execution with the privileges of the web server process, which typically runs as root on embedded devices like the Tenda AC9.

Root Cause

The root cause of this vulnerability is insufficient input validation in the formGetRebootTimer function. The function accepts time parameter values through the web interface but does not properly verify that the input length falls within expected bounds before performing memory copy operations. This lack of boundary checking allows maliciously crafted input to overflow the destination buffer on the stack.

Attack Vector

The attack vector is network-based, requiring the attacker to have authenticated access to the router's administrative web interface. The exploitation process involves:

1. Authenticating to the Tenda AC9 router's web management interface
2. Sending a crafted HTTP request to the endpoint handling the formGetRebootTimer function
3. Including oversized values in the sys.schedulereboot.start_time or sys.schedulereboot.end_time parameters
4. The malformed input overflows the stack buffer, corrupting the return address
5. Control flow is redirected to execute arbitrary code or crash the device

The vulnerability has been publicly disclosed with technical details available in the GitHub IoT Vulnerability Report. Since the exploit affects the router's core firmware functionality, successful exploitation could allow complete device compromise.

Detection Methods for CVE-2026-2192

Indicators of Compromise

• Unexpected router reboots or crashes, particularly when accessing reboot scheduler functionality
• Abnormal HTTP POST requests to the router's web interface containing unusually long parameter values
• Anomalous network traffic originating from the router to external destinations following administrative access
• Unexplained changes to router configuration or firmware settings

Detection Strategies

• Monitor web server logs on the Tenda AC9 for requests containing abnormally long values in sys.schedulereboot.start_time or sys.schedulereboot.end_time parameters
• Implement network intrusion detection rules to identify HTTP requests with oversized form parameters targeting Tenda router management interfaces
• Deploy endpoint detection and response (EDR) solutions capable of monitoring IoT device behavior for anomalous activity
• Review authentication logs for unauthorized administrative access attempts to router management interfaces

Monitoring Recommendations

• Establish baseline network behavior for the Tenda AC9 router and alert on deviations
• Implement segmentation to isolate IoT devices from critical network assets
• Enable logging on the router if supported and forward logs to a centralized SIEM for analysis
• Regularly audit administrative access to network infrastructure devices

How to Mitigate CVE-2026-2192

Immediate Actions Required

• Restrict administrative access to the Tenda AC9 web interface to trusted IP addresses only
• Disable remote management functionality if not required for business operations
• Implement strong, unique administrative credentials for the router
• Consider placing the router behind a firewall with strict access controls
• Monitor for firmware updates from Tenda and apply patches immediately when available

Patch Information

At the time of publication, no official patch has been released by Tenda for this vulnerability. Users should monitor the Tenda Official Website for security updates and firmware releases. Additional technical details are available through VulDB #344895.

Workarounds

• Disable the scheduled reboot timer functionality if not actively required
• Implement network-level access controls to restrict which hosts can reach the router's administrative interface
• Use a VPN or jump host architecture to provide secure administrative access rather than exposing the management interface directly
• Consider replacing vulnerable devices with alternatives that receive regular security updates

# Example: Restrict administrative access via firewall rules
# Block external access to router management port (typically 80/443)
iptables -A INPUT -p tcp --dport 80 -s !192.168.1.0/24 -j DROP
iptables -A INPUT -p tcp --dport 443 -s !192.168.1.0/24 -j DROP