CVE-2026-4490: Tenda A18 Pro Buffer Overflow Vulnerability

CVE-2026-4490 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda A18 Pro firmware version 02.03.02.28. The vulnerability exists in the setSchedWifi function within the /goform/openSchedWifi endpoint. Successful exploitation of this vulnerability allows remote attackers to cause a buffer overflow condition, potentially leading to arbitrary code execution or denial of service on affected devices.

Critical Impact

Remote attackers can exploit this stack-based buffer overflow to compromise Tenda A18 Pro wireless routers, potentially gaining unauthorized control over the device and the network it manages.

Affected Products

• Tenda A18 Pro firmware version 02.03.02.28

Discovery Timeline

• 2026-03-20 - CVE-2026-4490 published to NVD
• 2026-03-24 - Last updated in NVD database

Technical Details for CVE-2026-4490

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer). The setSchedWifi function in the Tenda A18 Pro firmware fails to properly validate the length of user-supplied input before copying it into a fixed-size stack buffer. This lack of boundary checking allows an attacker to supply oversized input data that exceeds the allocated buffer size, overwriting adjacent memory on the stack.

The exploit has been publicly disclosed and documented, increasing the risk of active exploitation. The network-accessible nature of this vulnerability means that any attacker with network access to the device's web management interface can attempt exploitation without requiring physical access.

Root Cause

The root cause of this vulnerability is improper input validation in the setSchedWifi function. The function processes data received through the /goform/openSchedWifi endpoint without adequately checking the size of incoming parameters against the buffer capacity allocated on the stack. This classic buffer overflow pattern allows attackers to overwrite return addresses, saved registers, or other critical stack data structures.

Attack Vector

The attack vector is network-based, requiring the attacker to send specially crafted HTTP requests to the vulnerable endpoint /goform/openSchedWifi. The attack requires low privileges (authenticated access to the router's web interface) but no user interaction. An attacker can craft malicious input parameters designed to overflow the stack buffer within the setSchedWifi function.

The exploitation technique typically involves:

1. Identifying the vulnerable endpoint and function
2. Crafting an oversized payload that exceeds the stack buffer bounds
3. Including shellcode or return-oriented programming (ROP) chains to redirect execution
4. Sending the malicious request to gain control of the affected device

Technical details and proof-of-concept information have been documented in the GitHub Issue Tracker. Additional vulnerability information is available through VulDB #352016.

Detection Methods for CVE-2026-4490

Indicators of Compromise

• Unusual or malformed HTTP POST requests to /goform/openSchedWifi endpoint
• Abnormally large parameter values in requests to the scheduled WiFi configuration interface
• Router crashes, unexpected reboots, or unresponsive web management interface
• Suspicious outbound connections from the router to unknown external IP addresses

Detection Strategies

• Monitor HTTP traffic to Tenda A18 Pro devices for requests containing oversized parameters targeting /goform/openSchedWifi
• Implement network intrusion detection rules to identify buffer overflow attack patterns against embedded device web interfaces
• Deploy anomaly detection to flag unusually large HTTP request bodies destined for router management endpoints
• Review router logs for authentication attempts followed by crashes or service disruptions

Monitoring Recommendations

• Enable logging on the Tenda A18 Pro device if supported and forward logs to a centralized SIEM
• Monitor for unexpected changes in router configuration or firmware
• Implement network segmentation to restrict access to router management interfaces from untrusted network segments
• Use SentinelOne Singularity to monitor network traffic patterns for exploitation attempts against IoT and embedded devices

How to Mitigate CVE-2026-4490

Immediate Actions Required

• Restrict network access to the router's web management interface to trusted IP addresses only
• Disable remote management access from WAN interfaces if not required
• Place affected Tenda A18 Pro devices behind a firewall with strict ingress filtering
• Monitor for firmware updates from Tenda and apply patches as soon as available

Patch Information

At the time of publication, no official patch information has been released by Tenda. Users are advised to monitor the Tenda Official Website for security updates and firmware releases addressing this vulnerability. Additional tracking information is available through VulDB CTI ID #352016.

Workarounds

• Implement access control lists (ACLs) to restrict access to the /goform/openSchedWifi endpoint
• Configure firewall rules to block external access to the router's management port (typically port 80 or 443)
• Consider disabling the scheduled WiFi feature if not required until a patch is available
• Use a VPN or secure tunnel if remote management access is necessary

# Example firewall rule to restrict management access (adjust for your environment)
# 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