CVE-2021-20157 in AC2600 TEW-827DRU
Summary
by MITRE • 12/31/2021
It is possible for an unauthenticated, malicious user to force the device to reboot due to a hidden administrative command.
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Analysis
by VulDB Data Team • 01/05/2022
This vulnerability represents a critical security flaw in network device firmware that allows unauthenticated attackers to remotely trigger device reboots through a hidden administrative command. The issue stems from improper access control mechanisms within the device's command processing subsystem, where certain administrative functions remain accessible without proper authentication. The vulnerability specifically affects devices that implement a command-line interface or remote management protocols, where the hidden command can be invoked through network-based attacks. This flaw demonstrates a fundamental failure in the principle of least privilege and authentication enforcement, creating a backdoor-like condition that bypasses normal security controls.
The technical implementation of this vulnerability involves a hidden administrative command that exists within the device's firmware but is not properly secured or documented. Attackers can exploit this by sending specifically crafted network requests or commands that trigger the hidden administrative function, which then executes a system reboot operation. This typically occurs through protocols such as telnet, ssh, or proprietary management interfaces where the command parsing logic fails to properly validate authentication status before executing privileged operations. The vulnerability is particularly concerning because it operates silently without requiring any valid credentials, making detection extremely difficult. This type of flaw is classified as a CWE-284 (Improper Access Control) and aligns with ATT&CK technique T1068 (Local Privilege Escalation) when exploited locally, or T1566 (Phishing) when used in social engineering contexts.
The operational impact of this vulnerability extends beyond simple service disruption to potentially enable more sophisticated attack vectors. While the immediate effect is a denial of service through unauthorized device reboots, this vulnerability can serve as a foundation for additional attacks. Repeated exploitation can cause persistent service degradation, create opportunities for privilege escalation, or provide attackers with timing windows for more complex attacks. The vulnerability is particularly dangerous in network infrastructure devices where device availability is critical for business operations, as unauthorized reboots can disrupt network connectivity, cause data loss, and create opportunities for further exploitation. This type of vulnerability directly impacts availability as defined by the CIA triad and can be leveraged as part of broader attack campaigns targeting network infrastructure.
Organizations should implement immediate mitigations including firmware updates from vendors, network segmentation to isolate affected devices, and monitoring for unauthorized command execution attempts. Network administrators should disable unnecessary administrative interfaces, implement strict access control lists, and configure intrusion detection systems to monitor for suspicious command patterns. The vulnerability highlights the importance of proper security testing and code review practices, particularly focusing on authentication mechanisms and command validation. Regular security assessments should include testing for hidden administrative functions and backdoors, while security teams should maintain comprehensive incident response procedures for handling unauthorized device reboots. Additionally, organizations should consider implementing device integrity monitoring solutions and ensuring that all administrative functions require proper authentication and authorization before execution. This vulnerability demonstrates the critical need for defense in depth strategies and proper access control implementation across all network infrastructure components.