CVE-2019-3910 in AM-100
Summary
by MITRE
Crestron AM-100 before firmware version 1.6.0.2 contains an authentication bypass in the web interface's return.cgi script. Unauthenticated remote users can use the bypass to access some administrator functionality such as configuring update sources and rebooting the device.
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Analysis
by VulDB Data Team • 05/03/2020
The CVE-2019-3910 vulnerability affects Crestron AM-100 devices running firmware versions prior to 1.6.0.2, representing a critical authentication bypass flaw that undermines the security posture of these networked control systems. This vulnerability specifically targets the web interface's return.cgi script, which serves as a gateway for administrative functions within the device's management interface. The flaw allows unauthenticated remote attackers to bypass the intended authentication mechanisms and gain access to sensitive administrative capabilities. The vulnerability is particularly concerning because it enables attackers to perform high-privilege operations without requiring valid credentials, effectively undermining the device's access control model.
The technical implementation of this authentication bypass occurs within the return.cgi script where the device fails to properly validate user authentication status before executing administrative commands. This weakness creates a pathway for remote exploitation where attackers can craft specific HTTP requests to access administrative functions such as configuring update sources and rebooting the device. The vulnerability stems from inadequate input validation and authentication checks within the web application layer, allowing attackers to manipulate the application flow to bypass standard authentication procedures. This type of flaw typically falls under CWE-287, which addresses improper authentication issues in software applications, and represents a classic example of a broken authentication vulnerability that enables privilege escalation.
The operational impact of this vulnerability extends beyond simple unauthorized access, as it provides attackers with the ability to compromise the entire device lifecycle management process. Attackers can manipulate update sources to deploy malicious firmware, potentially leading to complete device compromise or persistent backdoor access. The ability to reboot the device remotely creates additional attack vectors for denial-of-service scenarios or can be combined with other exploits to disrupt critical control systems. In enterprise environments where Crestron AM-100 devices are deployed for building automation and control, this vulnerability can lead to unauthorized modification of critical system configurations, potentially affecting security systems, lighting controls, audiovisual equipment, and other integrated building management functions. The vulnerability aligns with ATT&CK technique T1078.004, which covers valid accounts for privilege escalation and persistence within networked environments.
Mitigation strategies for CVE-2019-3910 primarily focus on immediate firmware updates to version 1.6.0.2 or later, which contain the necessary authentication fixes. Network segmentation should be implemented to isolate these devices from general network traffic, reducing the attack surface for remote exploitation attempts. Access controls should be enforced through firewall rules that restrict web interface access to trusted IP addresses only, while implementing strong network monitoring to detect suspicious authentication attempts. Regular security assessments should be conducted to identify other potentially vulnerable devices within the network infrastructure, as similar authentication bypass vulnerabilities may exist in other Crestron products. Organizations should also implement network intrusion detection systems capable of identifying malicious requests targeting the return.cgi script and establish incident response procedures for rapid remediation of affected devices. The vulnerability demonstrates the importance of maintaining up-to-date firmware in embedded systems and highlights the need for proper authentication design in networked control systems, as outlined in NIST SP 800-128 guidelines for embedded system security.