CVE-2018-0123 in IOS
Summary
by MITRE
A Path Traversal vulnerability in the diagnostic shell for Cisco IOS and IOS XE Software could allow an authenticated, local attacker to use certain diagnostic shell commands that can overwrite system files. These system files may be sensitive and should not be able to be overwritten by a user of the diagnostic shell. The vulnerability is due to lack of proper input validation for certain diagnostic shell commands. An attacker could exploit this vulnerability by authenticating to the device, entering the diagnostic shell, and providing crafted user input to commands at the local diagnostic shell CLI. Successful exploitation could allow the attacker to overwrite system files that should be restricted. Cisco Bug IDs: CSCvg41950.
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Analysis
by VulDB Data Team • 02/02/2021
The vulnerability described in CVE-2018-0123 represents a critical path traversal flaw within the diagnostic shell component of Cisco IOS and IOS XE software implementations. This security weakness specifically targets the diagnostic shell functionality that provides privileged access to system-level operations for troubleshooting purposes. The diagnostic shell serves as a specialized command-line interface that allows authorized personnel to perform deep system diagnostics and maintenance tasks, but this particular vulnerability creates an unauthorized pathway for file manipulation that bypasses normal access controls. The flaw manifests when the diagnostic shell fails to properly validate user input provided to specific commands, creating opportunities for attackers to craft malicious inputs that can traverse file system boundaries and access restricted areas of the device's file structure. This vulnerability is particularly concerning because it operates within a legitimate administrative interface, making it difficult to distinguish between authorized and malicious activities.
The technical exploitation of this vulnerability relies on the absence of proper input validation mechanisms within the diagnostic shell's command processing functions. When an authenticated user accesses the diagnostic shell and submits crafted commands containing path traversal sequences such as double dots or directory separators, the system fails to sanitize these inputs before executing the underlying file operations. This lack of input sanitization allows attackers to manipulate file paths and gain write access to system-critical files that should remain protected from modification. The vulnerability specifically affects commands that handle file operations within the diagnostic shell environment, where the system does not properly validate whether the requested file operations are within the intended scope of permissible actions. Attackers can leverage this weakness to overwrite essential system files, potentially leading to system instability, privilege escalation, or complete system compromise. The vulnerability is categorized under CWE-22 Path Traversal and aligns with ATT&CK technique T1059.001 Command and Scripting Interpreter, specifically targeting local system access and privilege escalation vectors.
The operational impact of CVE-2018-0123 extends beyond simple file modification capabilities to encompass potential system integrity compromise and operational disruption. An attacker who successfully exploits this vulnerability could overwrite critical system files including configuration files, binaries, or security-related components that maintain the device's operational integrity and security posture. This capability could enable attackers to disable security features, modify system behavior, or create persistent backdoors within the network infrastructure. The vulnerability affects Cisco IOS and IOS XE software versions where the diagnostic shell functionality has not been properly hardened against malicious input injection. The attack requires local authentication access, which means that the attacker must already have valid credentials to access the device, but this requirement does not significantly reduce the threat level since the diagnostic shell typically provides elevated privileges. The potential for system instability increases significantly when critical system files are overwritten, potentially causing device crashes, service interruptions, or complete loss of network connectivity for the affected device.
Organizations should implement multiple layers of mitigation strategies to address this vulnerability effectively. Immediate remediation efforts should focus on applying the relevant Cisco security patches and updates that address the input validation deficiencies in the diagnostic shell component. Network administrators should also consider implementing strict access controls and monitoring procedures to detect unauthorized access attempts to the diagnostic shell environment. The principle of least privilege should be enforced by limiting diagnostic shell access to only essential personnel with verified authorization requirements. Additionally, regular security audits should examine the configuration and usage of diagnostic shell commands to identify any potential misuse patterns or unauthorized access attempts. System monitoring should be enhanced to track file modification activities, particularly those involving system-critical files, and to correlate these activities with authentication events. Organizations should also review their overall security posture to ensure that diagnostic shell access is properly logged and audited, as this functionality often operates outside normal monitoring procedures. The vulnerability demonstrates the importance of input validation in privileged system interfaces and highlights the need for comprehensive security testing of administrative functions within network operating systems.