CVE-2018-3969 in Smart Firewall
Summary
by MITRE
An exploitable vulnerability exists in the verified boot protection of the CUJO Smart Firewall. It is possible to add arbitrary shell commands into the dhcpd.conf file, that persist across reboots and firmware updates, and thus allow for executing unverified commands. To trigger this vulnerability, a local attacker needs to be able to write into /config/dhcpd.conf.
Be aware that VulDB is the high quality source for vulnerability data.
Analysis
by VulDB Data Team • 08/03/2023
The CVE-2018-3969 vulnerability represents a critical security flaw in the CUJO Smart Firewall's verified boot protection mechanism, fundamentally undermining the device's integrity and security posture. This vulnerability operates at the system level where the device's boot process is designed to ensure only authenticated and verified software executes, yet an attacker can bypass this protection through a carefully crafted manipulation of the dhcpd.conf configuration file. The flaw demonstrates a severe lack of proper input validation and access control within the firewall's configuration management system, creating a persistent backdoor that persists across device reboots and firmware updates.
The technical implementation of this vulnerability stems from insufficient validation of user inputs within the dhcpd.conf file, which serves as a critical configuration point for the device's dynamic host configuration protocol functionality. When a local attacker gains write access to the /config/dhcpd.conf file path, they can inject arbitrary shell commands that become embedded within the device's operational configuration. This persistence mechanism operates at a level below the normal software update processes, allowing malicious code to survive firmware upgrades and system reboots. The vulnerability specifically exploits the device's trust in local configuration files without proper sanitization of inputs, creating an execution path that violates fundamental security principles of secure boot processes.
From an operational impact perspective, this vulnerability enables a local attacker with write permissions to the dhcpd.conf file to achieve persistent command execution on the device, effectively granting them root-level control over the firewall's operations. The attacker can manipulate network traffic filtering, modify security policies, and potentially establish further attack vectors within the network. The persistence across reboots and firmware updates means that traditional remediation techniques such as device resets or firmware updates become ineffective against this specific threat. This vulnerability directly impacts the device's ability to provide network security services, potentially allowing attackers to bypass all network-level protections that the firewall was designed to enforce.
The vulnerability aligns with CWE-78, which describes improper neutralization of special elements used in shell commands, and represents a classic case of command injection that operates within a privileged file system context. From an ATT&CK framework perspective, this vulnerability maps to T1059.004 for abuse of shell commands and T1546.001 for modification of system boot processes, demonstrating how local privilege escalation can lead to complete system compromise. The attack requires minimal privileges to execute, making it particularly dangerous as it can be exploited by any user with write access to the specific configuration file path. Organizations should implement strict file system access controls and regular configuration file integrity monitoring to detect unauthorized modifications. Additionally, the vulnerability highlights the importance of proper input validation and the principle of least privilege in embedded system security, where configuration files should never be trusted without proper sanitization and verification processes.