A recently uncovered authentication bypass vulnerability has exposed numerous NETGEAR DGND3700v2 routers to potential remote attacks, enabling cybercriminals to gain complete administrative control without the need for valid credentials. This flaw, identified as CVE-2025-4978 and assigned a critical CVSS score of 9.3, stands as one of the most severe router security issues identified in recent years.
Understanding the Vulnerability
The root of this vulnerability lies within the router’s embedded mini_http server, a lightweight HTTP daemon responsible for managing the device’s administrative web interface. Security researcher at0de discovered that accessing a specific unauthenticated endpoint, `/BRS_top.html`, triggers a critical security bypass mechanism.
When this endpoint is accessed, the system sets an internal variable named `start_in_blankstate` to 1, fundamentally altering the device’s authentication behavior. This flag is subsequently referenced in the `sub_404930` function, which handles HTTP Basic Authentication verification processes. If `start_in_blankstate` is set to 1, the verification is skipped, allowing users to access all features without proper permissions. This behavior suggests the presence of a backdoor mechanism rather than an accidental coding error.
Affected Devices and Firmware
The vulnerability specifically affects NETGEAR DGND3700v2 routers running firmware version V1.1.00.15_1.00.15NA. The mini_http server’s authentication logic in the `sub_406058` function processes all incoming HTTP requests, making this bypass particularly dangerous as it compromises the core security mechanism of the device.
Risk Factors and Exploit Prerequisites
– Affected Products: NETGEAR DGND3700v2 routers with firmware version V1.1.00.15_1.00.15NA.
– Impact: Full administrative access to the router’s configuration interface.
– Exploit Prerequisites:
– Access to the router’s web interface (either through the local network or exposed remote management).
– No authentication required.
– Ability to send an HTTP GET request to the `/BRS_top.html` endpoint.
– CVSS Score: 9.3 (Critical).
Security Implications
The simplicity of this exploit is particularly concerning for cybersecurity professionals. Attackers need only send a GET request to the vulnerable endpoint to disable authentication checks entirely. Once triggered, the bypass remains active until the device is rebooted or manually reset, providing persistent unauthorized access.
By accessing the unauthenticated endpoint `/BRS_top.html`, the internal flag `start_in_blankstate` is set to 1, which disables HTTP Basic Authentication checks. This mechanism allows attackers to:
– Modify DNS settings to redirect traffic.
– Install persistent malware.
– Harvest credentials from connected devices.
– Disable critical security features, including firewalls and parental controls.
The vulnerability can be exploited both from local networks and remotely when the router’s management interface is exposed to the internet. A proof-of-concept exploit named Longue vue demonstrates the attack’s effectiveness, capable of compromising devices directly through web browsers.
Recommendations and Mitigation
NETGEAR has stated: NETGEAR will not release a fix for this vulnerability on the affected product as the product is outside of the security support period. Current in-support models are not affected by this vulnerability. Despite this, the company has released firmware version 1.1.00.26 that addresses the vulnerability, contradicting their earlier statement about not providing fixes for out-of-support products.
Given the severity of the vulnerability and the potential for exploitation, users of the affected routers are strongly advised to take the following actions:
1. Update Firmware: If possible, update the router’s firmware to version 1.1.00.26 or later, which addresses the vulnerability. This can be done by visiting the NETGEAR support website, entering the router model number, and following the provided instructions for downloading and installing the latest firmware.
2. Disable Remote Management: If remote management is enabled, disable it to prevent unauthorized access from external networks. This setting can typically be found in the router’s administrative interface under the Remote Management section.
3. Change Default Credentials: Ensure that the default administrative username and password have been changed to strong, unique credentials. This reduces the risk of unauthorized access in case other vulnerabilities are present.
4. Monitor Network Activity: Regularly review the router’s logs and connected devices to identify any unusual activity that may indicate a compromise.
5. Consider Replacing Outdated Hardware: If the router is no longer supported by the manufacturer and cannot receive security updates, consider replacing it with a newer model that receives regular firmware updates and security patches.
Broader Context of Router Vulnerabilities
This incident is not isolated. NETGEAR routers have been subject to multiple vulnerabilities over the years. For instance, in February 2025, NETGEAR addressed two critical vulnerabilities, internally tracked as PSV-2023-0039 and PSV-2021-0117, impacting multiple WiFi router models. These flaws included a remote code execution issue and an authentication bypass vulnerability, both of which could be exploited by unauthenticated attackers without user interaction.
Additionally, in April 2024, NETGEAR acknowledged an authentication bypass vulnerability (PSV-2023-0166) affecting certain routers, which required an attacker to have the WiFi password or an Ethernet connection to exploit. The company released firmware fixes for all affected products within the security support period.
These recurring vulnerabilities underscore the importance of regular firmware updates and proactive security measures to protect network devices from potential exploits.
Conclusion
The discovery of the CVE-2025-4978 vulnerability in NETGEAR DGND3700v2 routers highlights the critical need for users to remain vigilant about the security of their network devices. By promptly updating firmware, disabling unnecessary remote access features, and adhering to best security practices, users can significantly reduce the risk of unauthorized access and potential cyberattacks. As cyber threats continue to evolve, staying informed and proactive is essential in maintaining a secure network environment.
