CVE-2021-20119 in Surfboard SB8200
Summary
by MITRE • 11/09/2021
The password change utility for the Arris SurfBoard SB8200 can have safety measures bypassed that allow any logged-in user to change the administrator password.
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Analysis
by VulDB Data Team • 11/12/2021
The CVE-2021-20119 vulnerability affects the Arris SurfBoard SB8200 cable modem, which is widely deployed in residential and small business networks across numerous service provider installations. This device serves as a critical gateway for internet connectivity and network management, making it a prime target for attackers seeking persistent access to network infrastructures. The vulnerability specifically resides within the password change utility functionality, which is designed to allow legitimate users to modify their own credentials while maintaining proper access controls. However, the implementation contains a fundamental flaw that undermines the security model of the device.
The technical flaw manifests in the authentication and authorization mechanisms of the password change utility. When a user attempts to change a password, the system should verify that the requesting user has appropriate privileges and that the change is being made within the bounds of established security policies. In this case, the validation process fails to properly enforce administrative privilege requirements, allowing any user who has successfully authenticated to the device to execute administrative password changes without proper authorization. This represents a classic privilege escalation vulnerability where the system fails to properly validate the identity and permissions of the user attempting the action. The flaw essentially creates a backdoor path that bypasses the normal security controls designed to protect administrative functions from unauthorized access.
The operational impact of this vulnerability is significant and multifaceted across multiple threat scenarios. An attacker who gains initial access to the device through other means or even through social engineering could leverage this vulnerability to escalate privileges and gain full administrative control of the modem. This administrative access would allow the attacker to modify network configurations, disable security features, redirect traffic, and potentially establish persistent access points within the network. The vulnerability is particularly concerning because it affects devices that are often deployed in unsecured environments where physical access may be possible, and because many users may not be aware of the security implications of such a device. Additionally, since these modems are typically managed by service providers, the vulnerability could enable attackers to compromise entire customer networks, potentially affecting multiple users within a service provider's coverage area. The vulnerability also represents a potential attack vector for lateral movement within networks where the modem serves as a gateway device.
The vulnerability aligns with CWE-284, which describes improper access control, and can be mapped to ATT&CK technique T1078 for valid accounts and T1566 for social engineering, as the flaw enables attackers to gain administrative access through legitimate user accounts. Mitigation strategies should include immediate firmware updates from Arris to address the authentication bypass, network segmentation to limit access to administrative functions, and implementation of network monitoring to detect unauthorized administrative changes. Organizations should also consider disabling unnecessary administrative access ports and implementing multi-factor authentication where possible. Regular security assessments of network infrastructure devices are essential to identify similar vulnerabilities in other network equipment. Service providers should coordinate with their customers to ensure prompt patching and should consider implementing automated monitoring systems to detect unauthorized changes to network device configurations. The vulnerability demonstrates the critical importance of proper privilege validation in network infrastructure devices and highlights the need for comprehensive security testing throughout the device lifecycle.