CVE-2018-9249 in VDSL2 Modem HG 150-UB
Summary
by MITRE
FiberHome VDSL2 Modem HG 150-UB devices allow authentication bypass by ignoring the parent.location='login.html' JavaScript code in the response to an unauthenticated request.
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Analysis
by VulDB Data Team • 01/22/2020
The FiberHome HG 150-UB VDSL2 modem represents a common consumer-grade networking device that provides internet connectivity through digital subscriber line technology. These devices typically serve as the primary gateway between residential or small office networks and internet service providers, making them critical components in modern network infrastructure. The vulnerability described in CVE-2018-9249 specifically targets the authentication mechanism of this particular modem model, creating a significant security risk for users who rely on these devices for network access and protection.
This vulnerability manifests as an authentication bypass flaw that occurs when the device processes unauthenticated requests. The technical implementation involves the device's response to unauthorized access attempts where it fails to properly enforce authentication requirements. Specifically, the device ignores the JavaScript code parent.location='login.html' which is intended to redirect unauthenticated users to the login page. This JavaScript redirection mechanism serves as a fundamental security control that should prevent access to protected administrative interfaces until proper authentication credentials are provided.
The operational impact of this vulnerability extends beyond simple unauthorized access to encompass potential network compromise and data exposure. An attacker who successfully exploits this bypass can gain administrative access to the modem's web interface without providing valid credentials, potentially allowing them to modify network settings, change passwords, disable security features, or redirect traffic through malicious endpoints. This vulnerability directly violates the principle of least privilege and authentication requirements that form the foundation of network security. According to CWE-287, improper authentication represents one of the most critical security weaknesses in networked applications, as it allows unauthorized access to protected resources.
The attack surface for this vulnerability is particularly concerning given the widespread deployment of FiberHome modems in residential and small business environments. Many users lack the technical expertise to properly secure their networking equipment, making devices like the HG 150-UB attractive targets for attackers seeking to establish persistent access points within networks. The vulnerability aligns with ATT&CK technique T1078.004, which describes legitimate credentials usage through web application login pages, allowing adversaries to maintain access to network resources without detection. Network administrators may not immediately recognize the compromise since the device continues to function normally from a user perspective, while the attacker silently gains administrative privileges.
Mitigation strategies should focus on immediate firmware updates from FiberHome or the device manufacturer, as these updates typically contain patches for known authentication bypass vulnerabilities. Network segmentation and firewall rules can help limit the exposure of these devices to external threats, while regular monitoring of device access logs can help detect unauthorized access attempts. Organizations should implement proper network hygiene practices including regular vulnerability assessments, disabling unnecessary services, and ensuring that all network devices receive timely security updates. The vulnerability also highlights the importance of proper input validation and authentication enforcement in web applications, as the device's failure to respect the authentication redirect mechanism represents a fundamental flaw in its security architecture.