CVE-2017-12340 in NX-OS
Summary
by MITRE
A vulnerability in Cisco NX-OS System Software running on Cisco MDS Multilayer Director Switches, Cisco Nexus 7000 Series Switches, and Cisco Nexus 7700 Series Switches could allow an authenticated, local attacker to access the Bash shell of an affected device's operating system, even if the Bash shell is disabled on the system. The vulnerability is due to insufficient sanitization of user-supplied parameters that are passed to certain functions of the Python scripting sandbox of the affected system. An attacker could exploit this vulnerability to escape the scripting sandbox and enter the Bash shell of the operating system with the privileges of the authenticated user for the affected system. To exploit this vulnerability, the attacker must have local access to the affected system and be authenticated to the affected system with administrative or Python execution privileges. Cisco Bug IDs: CSCvd86513.
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Analysis
by VulDB Data Team • 12/11/2019
This vulnerability represents a critical privilege escalation flaw in Cisco NX-OS software affecting multiple high-end switching platforms including MDS Multilayer Director Switches and Nexus 7000/7700 Series switches. The issue stems from inadequate input validation within the Python scripting sandbox environment, creating a pathway for authenticated local attackers to bypass security controls and gain access to the underlying Bash shell. The vulnerability specifically targets the sanitization of user-supplied parameters passed to Python functions, which allows malicious input to escape the controlled scripting environment and execute with elevated privileges. This represents a fundamental failure in sandbox isolation mechanisms that should prevent unauthorized access to system-level shells.
The technical exploitation of this vulnerability requires an attacker to possess legitimate administrative credentials or Python execution privileges on the target system, making it a local privilege escalation vulnerability rather than a remote attack vector. However, the impact remains severe as the attacker can leverage their authenticated access to escalate privileges and gain full shell access to the operating system with the same privileges as the authenticated user. The vulnerability exists within the Python scripting sandbox implementation, where insufficient parameter sanitization allows crafted inputs to manipulate the execution flow and escape the restricted environment. This type of vulnerability aligns with CWE-74 which describes "Improper Neutralization of Special Elements in Output Used by a Downstream Component" and CWE-20 which addresses "Improper Input Validation" in software systems.
From an operational perspective, this vulnerability poses significant risk to enterprise network infrastructure as it allows attackers with minimal privileges to gain full system access through a local authenticated session. The attack requires physical or network access to the device with valid administrative credentials, but once exploited, provides complete control over the switching infrastructure including access to all network traffic flows, configuration data, and potential lateral movement capabilities. The vulnerability affects critical network equipment that often serves as core infrastructure components, making the potential impact far-reaching for enterprise security. Network defenders must understand that this vulnerability can be exploited to establish persistent access points within the network and potentially compromise other connected systems through the compromised switch.
Organizations should implement immediate mitigation strategies including applying the relevant Cisco security patches and updates released in response to this vulnerability. Network segmentation and access control measures should be strengthened to limit local access to these critical devices, while monitoring should be enhanced to detect unauthorized authentication attempts or shell access patterns. The vulnerability highlights the importance of proper sandbox implementation and input validation in privileged execution environments. Security teams should also consider implementing privileged access management solutions and regular vulnerability assessments to identify similar sandbox escape vulnerabilities. Additionally, network administrators should disable unnecessary services and limit the Python scripting capabilities on these devices where possible, following the principle of least privilege to minimize the potential impact of such vulnerabilities. The ATT&CK framework categorizes this as a privilege escalation technique through sandbox escape, making it particularly concerning for security operations centers that monitor for such activities.