CVE-2026-5609: Tenda i12 Buffer Overflow Vulnerability

CVE-2026-5609 Overview

A stack-based buffer overflow vulnerability has been discovered in Tenda i12 router firmware version 1.0.0.11(3862). The vulnerability exists in the formwrlSSIDset function within the /goform/wifiSSIDset endpoint of the Parameter Handler component. Improper handling of the index and wl_radio arguments allows remote attackers to trigger a buffer overflow condition, potentially leading to remote code execution or denial of service.

Critical Impact

This network-accessible vulnerability allows authenticated attackers to overflow stack memory buffers through manipulation of WiFi SSID configuration parameters, potentially compromising the entire router and connected network infrastructure.

Affected Products

• Tenda i12 Firmware version 1.0.0.11(3862)

Discovery Timeline

• 2026-04-06 - CVE CVE-2026-5609 published to NVD
• 2026-04-07 - Last updated in NVD database

Technical Details for CVE-2026-5609

Vulnerability Analysis

This vulnerability is classified under CWE-119 (Improper Restriction of Operations within the Bounds of a Memory Buffer), indicating a fundamental boundary checking failure in the firmware's parameter handling code. The formwrlSSIDset function processes user-supplied input from WiFi configuration requests without adequate length validation, allowing attackers to write beyond the allocated stack buffer boundaries.

The affected component handles wireless SSID configuration through a web-based management interface. When processing the index or wl_radio parameters, the function copies user-controlled data into a fixed-size stack buffer without verifying that the input length does not exceed the buffer capacity. This classic stack-based buffer overflow can corrupt adjacent stack memory, including saved return addresses and function pointers.

Root Cause

The root cause of this vulnerability lies in insufficient input validation within the formwrlSSIDset function. The code fails to properly bounds-check the index and wl_radio parameters before copying them into stack-allocated buffers. This allows attackers to supply oversized input that overflows the intended buffer space, corrupting the stack frame and potentially enabling arbitrary code execution.

Embedded network devices like routers often have limited security hardening, lacking protections such as stack canaries or Address Space Layout Randomization (ASLR), which makes exploitation of buffer overflows more reliable on these platforms.

Attack Vector

The attack is remotely exploitable over the network through the router's web management interface. An authenticated attacker can send a specially crafted HTTP POST request to the /goform/wifiSSIDset endpoint with malicious values for the index or wl_radio parameters. The oversized parameter values trigger the buffer overflow in the formwrlSSIDset function.

The vulnerability mechanism involves crafting HTTP requests with oversized parameter values that exceed the expected buffer size. When the Parameter Handler processes these requests without proper bounds checking, the stack memory is corrupted. For detailed technical analysis, refer to the GitHub Vulnerability Documentation and VulDB entry #355400.

Detection Methods for CVE-2026-5609

Indicators of Compromise

• Unusual HTTP POST requests to /goform/wifiSSIDset with abnormally large parameter values
• Router crashes or unexpected reboots following web management access
• Suspicious network traffic patterns indicating exploitation attempts against the router management interface
• Unexpected changes to wireless configuration settings

Detection Strategies

• Monitor HTTP traffic to router management interfaces for requests containing oversized index or wl_radio parameters
• Implement network intrusion detection rules to flag POST requests to /goform/wifiSSIDset exceeding normal parameter lengths
• Review router logs for repeated access attempts to the WiFi configuration endpoint
• Deploy SentinelOne Singularity for IoT to monitor firmware-level anomalies on network devices

Monitoring Recommendations

• Enable logging on the router management interface if available to capture access attempts
• Segment IoT and network infrastructure devices from general network traffic for improved visibility
• Implement network-based anomaly detection to identify potential exploitation traffic patterns

How to Mitigate CVE-2026-5609

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if not required for operations
• Implement firewall rules to block external access to the router's management port (typically port 80/443)
• Monitor for firmware updates from Tenda that address this vulnerability

Patch Information

At the time of publication, no official patch from Tenda has been confirmed for this vulnerability. Organizations should monitor the Tenda Official Website for firmware updates addressing CVE-2026-5609. Review the VulDB entry for updated remediation information.

Workarounds

• Implement network segmentation to isolate vulnerable Tenda i12 devices from critical network segments
• Use access control lists (ACLs) to restrict management interface access to specific trusted IP addresses
• Consider replacing affected devices with alternative hardware if no patch becomes available
• Deploy a Web Application Firewall (WAF) in front of the management interface to filter malicious requests

# Example iptables rules to restrict management access
# Allow management access only from trusted admin subnet
iptables -A INPUT -p tcp --dport 80 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 80 -j DROP
iptables -A INPUT -p tcp --dport 443 -s 192.168.1.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP