CVE-2019-1730 in NX-OS
Summary
by MITRE
A vulnerability in the Bash shell implementation for Cisco NX-OS Software could allow an authenticated, local attacker to bypass the limited command set of the restricted Guest Shell and execute commands at the privilege level of a network-admin user outside of the Guest Shell. The attacker must authenticate with valid administrator device credentials. The vulnerability is due to the incorrect implementation of a CLI command that allows a Bash command to be incorrectly invoked on the Guest Shell CLI. An attacker could exploit this vulnerability by authenticating to the device and entering a crafted command at the Guest Shell prompt. A successful exploit could allow the attacker to issue commands that should be restricted by a Guest Shell account.
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Analysis
by VulDB Data Team • 09/19/2023
The vulnerability identified as CVE-2019-1730 represents a critical privilege escalation flaw within Cisco NX-OS Software that undermines the security boundaries of the restricted Guest Shell environment. This vulnerability specifically affects network devices running Cisco NX-OS software where the Guest Shell feature is enabled, creating a dangerous situation where authenticated administrators can bypass intended security restrictions. The flaw stems from improper handling of command execution within the Guest Shell context, allowing attackers to escalate their privileges beyond the intended limitations of the restricted shell environment.
The technical implementation of this vulnerability resides in the incorrect handling of CLI commands that are designed to invoke Bash commands within the Guest Shell interface. When an authenticated administrator enters specific crafted commands at the Guest Shell prompt, the system fails to properly validate or restrict the execution context, enabling the attacker to execute arbitrary commands with elevated privileges equivalent to those of a network-admin user. This represents a direct violation of the principle of least privilege that should govern restricted shell environments, as the vulnerability allows execution of commands that should be strictly confined to the Guest Shell's limited capabilities.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it fundamentally compromises the security architecture of Cisco network devices. An attacker with valid administrator credentials can exploit this flaw to execute commands that would normally be restricted, potentially leading to complete compromise of the network device. The vulnerability's exploitation requires only local authentication and does not necessitate network access or additional attack vectors, making it particularly dangerous as it can be leveraged by insiders or attackers who have already gained administrative access to the device. This scenario aligns with ATT&CK technique T1068 which covers "Exploitation for Privilege Escalation" and demonstrates how command injection vulnerabilities can be weaponized to bypass security controls.
The security implications of CVE-2019-1730 are particularly severe given that it operates within the context of a device that is already compromised by an authenticated administrator. This means that the vulnerability can be exploited by attackers who have legitimate administrative access, making detection more difficult and potentially allowing for prolonged undetected access. The flaw essentially creates a backdoor mechanism within the legitimate administrative interface, undermining trust in the device's security controls. Organizations using Cisco NX-OS software with Guest Shell enabled are particularly vulnerable, as the attack surface is expanded beyond what was intended by the security design of the restricted shell environment.
Mitigation strategies for this vulnerability should include immediate patching of affected Cisco NX-OS software versions, along with careful monitoring of Guest Shell usage and command execution logs. Network administrators should implement strict access controls and regularly audit administrative activities to detect potential exploitation attempts. The vulnerability also highlights the importance of proper input validation and command execution handling in privileged interfaces, as demonstrated by CWE-78 which covers "Improper Neutralization of Special Elements used in OS Command" and CWE-20 which addresses "Improper Input Validation." Organizations should also consider disabling Guest Shell functionality when it is not required, as this eliminates the attack surface entirely and provides an additional layer of defense against such privilege escalation attacks.