CVE-2025-69766: Tenda AX3 Router RCE Vulnerability

CVE-2025-69766 Overview

CVE-2025-69766 is a stack-based buffer overflow vulnerability affecting Tenda AX3 router firmware version v16.03.12.11. The vulnerability exists in the formGetIptv function due to improper handling of the citytag stack buffer, which can lead to memory corruption and potentially enable remote code execution. This firmware vulnerability in a consumer-grade router poses significant risk as it can be exploited over the network without authentication or user interaction.

Critical Impact

Successful exploitation of this stack-based buffer overflow allows remote attackers to corrupt memory and potentially execute arbitrary code on vulnerable Tenda AX3 routers, leading to complete device compromise.

Affected Products

• Tenda AX3 Router
• Tenda AX3 Firmware version v16.03.12.11

Discovery Timeline

• 2026-01-21 - CVE-2025-69766 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2025-69766

Vulnerability Analysis

This vulnerability is classified as CWE-121 (Stack-based Buffer Overflow), a memory corruption flaw where data written to a stack buffer exceeds its allocated size, overwriting adjacent memory including return addresses or other critical data structures. In the case of CVE-2025-69766, the formGetIptv function in the Tenda AX3 firmware fails to properly validate or bound input before copying it into the citytag stack buffer.

The network-accessible nature of this vulnerability is particularly concerning for router firmware, as routers often serve as the security perimeter for home and small business networks. Exploitation requires no privileges or user interaction, making it an attractive target for opportunistic attacks against IoT devices.

Root Cause

The root cause of CVE-2025-69766 lies in insufficient bounds checking within the formGetIptv function. When processing IPTV configuration requests, the function copies user-supplied data into a fixed-size stack buffer named citytag without verifying that the input length does not exceed the buffer's capacity. This classic buffer overflow pattern allows attackers to overwrite stack memory beyond the intended boundary.

Attack Vector

The vulnerability is exploitable via network access to the router's web management interface. An attacker can craft a malicious HTTP request targeting the formGetIptv endpoint with an oversized citytag parameter. When processed by the vulnerable function, the oversized input overflows the stack buffer, corrupting adjacent stack memory. Depending on the firmware's memory layout and security mitigations, attackers may be able to:

1. Overwrite the function's return address to redirect execution flow
2. Corrupt local variables or saved registers
3. Inject and execute shellcode if the stack is executable
4. Chain with other vulnerabilities for more sophisticated attacks

For detailed technical analysis of this vulnerability, refer to the Notion Analysis of Tenda AX3 Exploit.

Detection Methods for CVE-2025-69766

Indicators of Compromise

• Unexpected HTTP requests to the formGetIptv endpoint with unusually large parameter values
• Router crashes or unexpected reboots, potentially indicating exploitation attempts
• Anomalous outbound network connections from the router to unknown IP addresses
• Unexpected changes to router configuration or DNS settings
• Unusual CPU or memory utilization on the affected device

Detection Strategies

• Monitor web management interface logs for requests to formGetIptv with oversized citytag parameters
• Deploy network intrusion detection signatures to identify buffer overflow payload patterns in HTTP traffic to Tenda devices
• Implement firmware integrity monitoring to detect unauthorized modifications
• Use network behavior analysis to identify anomalous traffic patterns from router devices

Monitoring Recommendations

• Enable logging on the Tenda AX3 if available and forward logs to a centralized SIEM
• Monitor for HTTP requests with parameter lengths exceeding normal operational bounds
• Implement network segmentation to limit exposure of router management interfaces
• Conduct periodic firmware version audits to ensure vulnerable versions are identified

How to Mitigate CVE-2025-69766

Immediate Actions Required

• Restrict access to the router's web management interface to trusted internal networks only
• Disable remote management features if they are not required
• Implement firewall rules to block external access to the router's administrative ports
• Monitor for firmware updates from Tenda and apply them as soon as available
• Consider isolating vulnerable devices on a separate network segment

Patch Information

As of the last update on 2026-01-22, no official patch information has been published by Tenda. Organizations should monitor the vendor's support channels and security advisories for updates. The Notion Analysis of Tenda AX3 Exploit provides additional technical details that may assist in developing interim mitigations.

Workarounds

• Disable the IPTV functionality if it is not required for your deployment
• Use a firewall or access control list to restrict access to the router's web interface to specific trusted IP addresses
• Place the router behind a more secure network device that can filter malicious requests
• Consider replacing the affected device with a router from a vendor with a stronger security update track record
• Enable MAC address filtering as an additional layer of access control for the management interface

# Example: Restrict management interface access via iptables on an upstream device
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -s <TRUSTED_NETWORK> -j ACCEPT
iptables -A FORWARD -d <ROUTER_IP> -p tcp --dport 80 -j DROP