CVE-2019-1965 in NX-OS
Summary
by MITRE
A vulnerability in the Virtual Shell (VSH) session management for Cisco NX-OS Software could allow an authenticated, remote attacker to cause a VSH process to fail to delete upon termination. This can lead to a build-up of VSH processes that overtime can deplete system memory. When there is no system memory available, this can cause unexpected system behaviors and crashes. The vulnerability is due to the VSH process not being properly deleted when a remote management connection to the device is disconnected. An attacker could exploit this vulnerability by repeatedly performing a remote management connection to the device and terminating the connection in an unexpected manner. A successful exploit could allow the attacker to cause the VSH processes to fail to delete, which can lead to a system-wide denial of service (DoS) condition. The attacker must have valid user credentials to log in to the device using the remote management connection.
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Analysis
by VulDB Data Team • 12/07/2023
The vulnerability identified as CVE-2019-1965 represents a critical memory management flaw within Cisco NX-OS Software's Virtual Shell (VSH) session handling mechanism. This issue specifically targets the process cleanup routine that should automatically terminate and remove VSH processes upon disconnection of remote management sessions. The vulnerability operates at the system-level process management layer, where proper resource deallocation fails to occur, creating a persistent memory leak condition that can accumulate over time. The flaw manifests when remote management connections are terminated abruptly rather than gracefully, causing the underlying VSH processes to remain in memory indefinitely. This represents a classic denial of service vector that can be exploited by authenticated attackers who understand the timing and connection patterns required to trigger the memory accumulation behavior. The vulnerability directly impacts the stability and availability of network infrastructure devices running affected Cisco NX-OS versions, particularly those that handle frequent remote management sessions.
The technical implementation of this vulnerability stems from inadequate process lifecycle management within the VSH subsystem of Cisco NX-OS. When a remote management session is established and subsequently terminated unexpectedly, the system's process management routines fail to execute the proper cleanup sequence that would normally remove the VSH process from memory. This failure creates a resource leak scenario where each terminated connection leaves behind a zombie-like process that continues to consume system memory. The vulnerability is classified as a memory leak under CWE-404, specifically involving improper resource management where allocated resources are not properly released. The attack vector requires an authenticated user with valid credentials to establish remote management connections, making this a privilege-escalation related vulnerability that can be leveraged for denial of service attacks. The system's inability to properly handle connection termination events creates a persistent degradation of system resources that can eventually lead to complete system instability.
The operational impact of CVE-2019-1965 extends beyond simple resource consumption to encompass complete system availability compromise. As VSH processes accumulate over time, they consume increasing amounts of system memory, eventually leading to memory exhaustion conditions that can cause the device to become unresponsive or crash entirely. This memory depletion can affect other critical system processes and services, creating cascading failures that impact network connectivity and device functionality. The vulnerability is particularly dangerous in high-availability network environments where device uptime is critical, as the gradual accumulation of these processes can go unnoticed until system failures occur. Network administrators may observe performance degradation before complete system crashes, making this vulnerability difficult to detect and remediate in production environments. The DoS condition created by this vulnerability can be sustained over extended periods, potentially requiring device reboot to restore normal operation and clear the accumulated processes. The attack can be executed repeatedly with minimal resources, making it a persistent threat that can be maintained over time to continuously degrade system performance.
Mitigation strategies for CVE-2019-1965 should focus on both immediate remediation and long-term system hardening approaches. Cisco has released software updates and patches that address the process cleanup mechanism and ensure proper VSH process termination upon connection loss. Organizations should prioritize applying these patches to all affected devices in their network infrastructure to eliminate the vulnerability at its source. System monitoring should be implemented to track memory usage patterns and process counts for VSH sessions, enabling early detection of accumulation behaviors before they reach critical levels. Network administrators should establish connection management policies that enforce graceful disconnection procedures and implement automated monitoring solutions that can alert when process counts exceed normal thresholds. The vulnerability's classification under CWE-404 and its potential mapping to ATT&CK technique T1499.004 (Network Denial of Service) indicates that defense-in-depth strategies should include network segmentation and access control measures to limit the potential impact of authenticated attacks. Regular system audits and memory utilization monitoring should be implemented as part of ongoing security operations to prevent accumulation of vulnerable processes and maintain system stability. Additionally, implementing connection timeout mechanisms and automated process cleanup routines can provide additional protection against this specific vulnerability while maintaining operational efficiency.