CVE-2018-15368 in IOS XE
Summary
by MITRE
A vulnerability in the CLI parser of Cisco IOS XE Software could allow an authenticated, local attacker to gain access to the underlying Linux shell of an affected device and execute arbitrary commands with root privileges on the device. The vulnerability is due to the affected software improperly sanitizing command arguments to prevent modifications to the underlying Linux filesystem on a device. An attacker who has privileged EXEC mode (privilege level 15) access to an affected device could exploit this vulnerability on the device by executing CLI commands that contain crafted arguments. A successful exploit could allow the attacker to gain access to the underlying Linux shell of the affected device and execute arbitrary commands with root privileges on the device.
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Analysis
by VulDB Data Team • 03/30/2020
This vulnerability exists within the command line interface parser of Cisco IOS XE Software, representing a critical privilege escalation flaw that fundamentally undermines the security boundaries of network infrastructure devices. The issue stems from insufficient input validation and sanitization mechanisms within the CLI processing layer, which fails to properly filter or escape command arguments before they are passed to the underlying Linux operating system. This weakness creates an exploitable path where authenticated users with privileged EXEC mode access can manipulate command parameters to bypass intended security controls and gain unauthorized access to the device's native Linux shell environment.
The technical flaw manifests as a command injection vulnerability in the CLI parsing logic, where crafted arguments can modify the behavior of underlying system commands without proper sanitization. According to CWE-77, this represents a classic command injection vulnerability where user-supplied input is not properly validated or escaped before being executed by the system. The vulnerability specifically affects the parsing of command arguments in a way that allows attackers to manipulate the execution flow of CLI commands, ultimately enabling access to the underlying Linux shell through improper argument handling. Attackers can leverage this flaw by constructing specific CLI commands that contain malicious arguments, which when processed by the vulnerable parser, result in unintended execution of system commands with elevated privileges.
The operational impact of this vulnerability is severe and far-reaching, as it allows authenticated attackers with privilege level 15 access to achieve full system compromise and execute arbitrary code with root privileges. This represents a complete breakdown of the privilege model within Cisco IOS XE devices, where the normally secure boundary between user access and system-level operations is breached. The vulnerability enables attackers to perform actions such as modifying system files, installing malicious software, accessing sensitive data, and potentially using the compromised device as a pivot point for attacks against other network segments. The implications extend beyond immediate device compromise to include potential network-wide infiltration and persistent access that can remain undetected for extended periods.
Mitigation strategies must address both immediate protection and long-term security improvements for affected devices. Organizations should implement immediate access controls and monitoring to detect unusual CLI command patterns that might indicate exploitation attempts. The recommended approach includes applying Cisco's official security patches and updates as soon as they become available, which typically involve enhanced input validation and sanitization routines within the CLI parser. Network administrators should also consider implementing additional security measures such as restricted CLI access, logging and monitoring of privileged command execution, and regular security audits of device configurations. From an ATT&CK framework perspective, this vulnerability aligns with techniques such as privilege escalation and command and control, making it essential for security teams to monitor for indicators of compromise related to shell access and unauthorized system modifications. The vulnerability underscores the importance of proper input validation and the principle of least privilege in network security architectures, as it demonstrates how a single parsing flaw can enable complete system compromise.