CVE-2020-3403 in IOS XE
Summary
by MITRE
A vulnerability in the CLI of Cisco IOS XE Software could allow an authenticated, local attacker to inject a command to the underlying operating system that will execute with root privileges upon the next reboot of the device. The authenticated user must have privileged EXEC permissions on the device. The vulnerability is due to insufficient protection of values passed to a script that executes during device startup. An attacker could exploit this vulnerability by writing values to a specific file. A successful exploit could allow the attacker to execute commands with root privileges each time the affected device is restarted.
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Analysis
by VulDB Data Team • 09/25/2020
This vulnerability exists within the command line interface of Cisco IOS XE Software and represents a critical privilege escalation flaw that can be exploited by authenticated local attackers. The vulnerability stems from inadequate input validation and sanitization mechanisms within the device's startup script execution process. An attacker must possess privileged EXEC permissions on the device to exploit this flaw, which aligns with the common security principle that local privilege escalation vulnerabilities often require initial authentication to leverage. The vulnerability specifically affects the handling of values passed to scripts that execute during device startup, creating a persistent backdoor mechanism that survives device reboots. According to CWE classification, this vulnerability maps to CWE-78, which describes improper neutralization of special elements used in OS commands, indicating a command injection weakness in the system's startup process. The root cause lies in the insufficient protection of user-controllable values that are passed to system-level scripts during device initialization, creating a dangerous execution path for malicious commands.
The operational impact of this vulnerability is severe and persistent, as it allows an attacker to establish a root-level backdoor that executes automatically with each device reboot. This means that even if system administrators detect and remove malicious code from running processes, the malicious commands will persist and re-execute upon the next system restart. The attack vector requires an authenticated user with privileged EXEC permissions, which typically represents a compromised administrative account or an insider threat. The exploitation process involves writing malicious values to a specific file that is subsequently processed by the startup scripts, effectively creating a persistent command injection mechanism. This vulnerability undermines the fundamental security model of network devices by allowing local privilege escalation that persists across system reboots, making it particularly dangerous for network infrastructure security.
From an attack framework perspective, this vulnerability aligns with the MITRE ATT&CK technique T1068, which covers 'Exploitation for Privilege Escalation' and specifically addresses local privilege escalation through command injection. The vulnerability also demonstrates characteristics of T1059, 'Command and Scripting Interpreter,' as it allows execution of arbitrary commands through the underlying operating system. The persistent nature of this vulnerability makes it particularly attractive to attackers seeking long-term access to network infrastructure, as it provides a reliable method for maintaining root-level access across device restarts. Network security teams should consider this vulnerability as a potential indicator of compromise, especially when observing unusual system behavior or unauthorized changes to device configuration files that might be related to startup script modifications.
The recommended mitigations for this vulnerability include immediate implementation of the vendor-provided security patches and updates released by Cisco to address the command injection flaw in the startup script execution process. Network administrators should also implement strict access controls and monitoring of privileged EXEC sessions to detect unauthorized access attempts. Regular audit of startup script configuration files and system logs should be conducted to identify any suspicious modifications or command executions. Additionally, implementing network segmentation and least privilege principles can limit the potential impact of successful exploitation, while maintaining comprehensive logging and monitoring capabilities can help detect and respond to exploitation attempts. The vulnerability highlights the importance of secure coding practices in system initialization processes and the need for proper input validation and sanitization of all user-controllable data passed to system-level scripts during device startup operations.