CVE-2026-5830: Tenda AC15 Buffer Overflow Vulnerability

CVE-2026-5830 Overview

A stack-based buffer overflow vulnerability has been identified in Tenda AC15 wireless routers running firmware version 15.03.05.18. The vulnerability exists in the websGetVar function within the /goform/SysToolChangePwd endpoint, which handles password change requests. An attacker can exploit this flaw by manipulating the oldPwd, newPwd, or cfmPwd parameters to trigger a buffer overflow condition. This vulnerability can be exploited remotely over the network and a public exploit is reportedly available.

Critical Impact

Remote attackers with low-level privileges can exploit this stack-based buffer overflow to potentially execute arbitrary code, compromise router integrity, and gain complete control over the affected network device.

Affected Products

• Tenda AC15 Router with Firmware Version 15.03.05.18
• Tenda AC15 devices with /goform/SysToolChangePwd endpoint exposed

Discovery Timeline

• 2026-04-09 - CVE-2026-5830 published to NVD
• 2026-04-09 - Last updated in NVD database

Technical Details for CVE-2026-5830

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), which indicates that the affected firmware fails to properly validate the length of user-supplied input before copying it into a fixed-size buffer on the stack.

The vulnerable function websGetVar processes password-related parameters submitted through the web management interface at /goform/SysToolChangePwd. When a user or attacker submits excessively long values for the oldPwd, newPwd, or cfmPwd parameters, the function copies these values into stack buffers without adequate boundary checking. This allows the attacker to overwrite adjacent stack memory, including return addresses and saved registers.

The network-accessible nature of this vulnerability combined with the low attack complexity makes it particularly dangerous for exposed router management interfaces. Successful exploitation could lead to complete device compromise, allowing attackers to intercept network traffic, modify router configurations, or use the device as a pivot point for further attacks.

Root Cause

The root cause of this vulnerability lies in the unsafe handling of user-supplied string data in the password change functionality. The websGetVar function retrieves HTTP form parameters and stores them in stack-allocated buffers. The implementation lacks proper bounds checking to ensure that input data does not exceed the allocated buffer size.

When processing the oldPwd, newPwd, and cfmPwd parameters, the function uses unsafe string operations that do not account for the maximum buffer capacity. This allows attackers to provide maliciously crafted input that exceeds buffer boundaries, corrupting adjacent stack memory and potentially hijacking program execution flow.

Attack Vector

The attack is executed remotely over the network by sending a specially crafted HTTP POST request to the /goform/SysToolChangePwd endpoint. An attacker must have low-level privileges (authenticated access) to reach the password change functionality.

The exploitation process involves:

1. Establishing a connection to the router's web management interface
2. Authenticating with valid credentials to gain access to the password change form
3. Crafting a malicious HTTP POST request with oversized values in the oldPwd, newPwd, or cfmPwd parameters
4. Sending the request to trigger the stack buffer overflow
5. Depending on the payload, achieving denial of service or arbitrary code execution

The vulnerability is particularly concerning because router management interfaces are sometimes inadvertently exposed to the internet, and the public availability of exploit information increases the risk of widespread attacks.

Detection Methods for CVE-2026-5830

Indicators of Compromise

• Unexpected crashes or reboots of Tenda AC15 routers
• Suspicious HTTP POST requests to /goform/SysToolChangePwd with abnormally long parameter values
• Unusual network traffic patterns originating from or destined to the router's management interface
• Unauthorized configuration changes on affected devices

Detection Strategies

• Monitor web server logs for HTTP POST requests to /goform/SysToolChangePwd containing oversized payload data
• Implement intrusion detection rules to flag requests with oldPwd, newPwd, or cfmPwd parameters exceeding typical length thresholds
• Deploy network-based anomaly detection to identify buffer overflow attack patterns targeting embedded devices
• Utilize SentinelOne Singularity to detect exploitation attempts and post-compromise activity on network segments

Monitoring Recommendations

• Establish baseline monitoring for router management interface access patterns
• Configure alerting for failed authentication attempts followed by unusual POST requests
• Monitor for memory corruption signatures in network traffic targeting Tenda devices
• Regularly review router logs for evidence of exploitation attempts

How to Mitigate CVE-2026-5830

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management functionality if not required
• Implement network segmentation to isolate affected devices
• Monitor for exploitation attempts using network-based detection tools
• Consider replacing affected devices if firmware updates are not available

Patch Information

At the time of publication, no official patch has been confirmed from Tenda. Organizations should monitor the Tenda Official Website for firmware updates addressing this vulnerability. Additional technical details are available through VulDB Vulnerability #356277.

Users are strongly advised to contact Tenda support for guidance on remediation options and to subscribe to security notifications for the AC15 product line.

Workarounds

• Configure firewall rules to block external access to the router's management interface on port 80/443
• Implement access control lists (ACLs) to limit management interface access to specific trusted IP addresses
• Use VPN connections for remote management instead of exposing the web interface directly
• Deploy network intrusion prevention systems with signatures for buffer overflow attacks

# Example firewall rules to restrict management interface access
# Block external access to router management interface
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

# Allow management access only from trusted admin workstation
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.100 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.100 -j ACCEPT