CVE-2026-4252: Tenda AC8 Authentication Bypass Vulnerability

CVE-2026-4252 Overview

A critical authentication bypass vulnerability has been identified in Tenda AC8 routers running firmware version 16.03.50.11. The vulnerability exists in the check_is_ipv6 function within the IPv6 Handler component. Due to improper reliance on IP address for authentication (CWE-287), attackers can bypass authentication mechanisms and gain unauthorized access to the device remotely. A public proof-of-concept exploit has been disclosed, increasing the urgency for affected users to take protective measures.

Critical Impact

Unauthenticated remote attackers can bypass authentication controls on Tenda AC8 routers, potentially gaining full administrative access to the network device and compromising network security.

Affected Products

• Tenda AC8 Router - Firmware Version 16.03.50.11

Discovery Timeline

• 2026-03-16 - CVE-2026-4252 published to NVD
• 2026-03-17 - Last updated in NVD database

Technical Details for CVE-2026-4252

Vulnerability Analysis

This vulnerability stems from an improper authentication mechanism in the Tenda AC8 router's IPv6 handling functionality. The check_is_ipv6 function relies on IP address-based authentication, which is fundamentally flawed as IP addresses can be spoofed or manipulated by attackers.

The weakness allows remote attackers to circumvent authentication controls entirely without requiring valid credentials. Since the router exposes this functionality over the network interface, the attack surface is significant. Successful exploitation grants attackers unauthorized access to router management functions, potentially leading to complete device compromise, network configuration changes, traffic interception, or using the compromised router as a pivot point for further attacks within the network.

Root Cause

The root cause of this vulnerability lies in the flawed authentication design within the IPv6 Handler component. The check_is_ipv6 function incorrectly uses the client's IP address as an authentication factor instead of implementing proper credential-based authentication. This design flaw (CWE-287: Improper Authentication) allows attackers to bypass security controls by manipulating or spoofing their source IP address, or by accessing the vulnerable function from a trusted network position.

Attack Vector

The attack can be initiated remotely over the network. An attacker does not require prior authentication or user interaction to exploit this vulnerability. The attack methodology involves sending specially crafted requests to the IPv6 Handler component that exploit the IP address-based authentication weakness.

The vulnerability has been publicly disclosed with a proof-of-concept exploit available in a GitHub PoC Repository, making it accessible to a wide range of potential attackers. Technical details can also be found in the VulDB entry #351210.

Detection Methods for CVE-2026-4252

Indicators of Compromise

• Unexpected authentication events or successful logins from untrusted IP addresses in router logs
• Unauthorized changes to router configuration, especially IPv6 settings
• Anomalous network traffic patterns originating from or targeting the router management interface
• New or modified administrative accounts on the device

Detection Strategies

• Monitor router access logs for authentication attempts that bypass normal credential verification
• Implement network-based intrusion detection rules to identify exploitation attempts against the IPv6 Handler
• Deploy network traffic analysis to detect suspicious patterns targeting Tenda AC8 devices on management ports
• Review router configurations periodically for unauthorized modifications

Monitoring Recommendations

• Enable comprehensive logging on Tenda AC8 devices and forward logs to a centralized SIEM solution
• Implement alerting for any configuration changes on network infrastructure devices
• Monitor for reconnaissance activity targeting router management interfaces
• Track firmware versions across deployed Tenda devices to identify vulnerable systems

How to Mitigate CVE-2026-4252

Immediate Actions Required

• Restrict network access to the router management interface to trusted administrative IP addresses only
• Disable remote administration features if not required for operations
• Implement network segmentation to isolate vulnerable devices from untrusted networks
• Monitor for any signs of compromise using the detection methods outlined above

Patch Information

At the time of publication, no official patch from Tenda has been confirmed in the available CVE data. Users should monitor the Tenda official website for firmware updates addressing this vulnerability. Review the VulDB entry for the latest status on vendor response and patch availability.

Workarounds

• Implement firewall rules to block external access to the router's management interface
• Use a VPN or jump host for administrative access rather than exposing the management interface directly
• Consider replacing affected devices with alternative hardware if a patch is not made available in a timely manner
• Disable IPv6 functionality if not required for network operations as a temporary measure