CVE-2018-0156 in IOS
Summary
by MITRE
A vulnerability in the Smart Install feature of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to trigger a reload of an affected device, resulting in a denial of service (DoS) condition. The vulnerability is due to improper validation of packet data. An attacker could exploit this vulnerability by sending a crafted packet to an affected device on TCP port 4786. Only Smart Install client switches are affected. Cisco devices that are configured as a Smart Install director are not affected by this vulnerability. Cisco Bug IDs: CSCvd40673.
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Analysis
by VulDB Data Team • 01/27/2025
The vulnerability described in CVE-2018-0156 resides within the Smart Install feature of Cisco IOS and IOS XE software implementations, representing a significant security flaw that enables unauthorized remote attackers to disrupt network operations through deliberate device reloads. This vulnerability specifically targets Cisco switches configured as Smart Install clients, creating a critical denial of service condition that can severely impact network availability and operational continuity. The flaw manifests through improper validation of packet data received on TCP port 4786, which serves as the designated communication channel for Smart Install functionality within Cisco networking equipment. The vulnerability's remote exploitation capability means that attackers can initiate malicious activity from outside the network perimeter without requiring authentication credentials, making it particularly dangerous for enterprise and service provider environments where network availability is paramount.
The technical mechanism behind this vulnerability stems from inadequate input validation within the Smart Install client processing logic, which fails to properly sanitize or verify incoming packet data structures before attempting to process them. This weakness allows an attacker to craft malicious packets that, when transmitted to the vulnerable device on port 4786, trigger an unexpected system behavior resulting in automatic device reload. The specific nature of this flaw aligns with CWE-20, which describes "Improper Input Validation" as a fundamental weakness that enables various attack vectors including buffer overflows, injection attacks, and system manipulation. The vulnerability's exploitation requires minimal privileges since no authentication is required, making it accessible to any attacker who can reach the target device through network connectivity. The Smart Install feature was designed to facilitate automated software deployment and configuration management across Cisco networks, but this implementation contains a critical design flaw that undermines its security posture and introduces a potential attack surface for malicious actors.
The operational impact of CVE-2018-0156 extends beyond simple service disruption, as the automatic device reloads can cause cascading failures within network infrastructure, particularly in environments where redundant systems depend on synchronized operation or where automated failover mechanisms are triggered by device unavailability. Network administrators may experience extended downtime periods while devices restart and re-establish network connectivity, potentially disrupting business operations and requiring manual intervention to restore full network functionality. The vulnerability affects only Smart Install client switches, which means that devices configured as Smart Install directors remain unaffected, creating a differential security posture within the same network environment. This selective impact requires careful network segmentation and configuration management to ensure that only authorized devices operate in the Smart Install client role, while maintaining proper network architecture to prevent unauthorized access to vulnerable endpoints. The vulnerability's discovery highlights the importance of proper security testing for network management features and demonstrates how seemingly legitimate administrative functions can introduce security risks when not properly validated against malicious input.
Organizations affected by this vulnerability should implement immediate mitigation strategies including network segmentation to restrict access to TCP port 4786, deployment of access control lists to block unauthorized traffic, and consideration of disabling Smart Install functionality where it is not strictly required for network operations. Network security teams should also monitor for unusual traffic patterns or device reload events that might indicate exploitation attempts. The recommended approach involves configuring firewalls or access control lists to prevent external access to port 4786 on Smart Install client devices while ensuring that internal administrative access remains properly controlled. Additionally, Cisco has released software updates and patches to address this vulnerability, which should be applied promptly to eliminate the security risk. From an ATT&CK framework perspective, this vulnerability maps to techniques involving privilege escalation and denial of service, specifically leveraging network service vulnerabilities to achieve system manipulation. The mitigation strategies align with defensive measures outlined in the MITRE ATT&CK framework for network service hardening and access control implementation, emphasizing the need for proper network architecture design and security controls to prevent unauthorized access to critical network management functions. Organizations should also consider implementing network monitoring solutions that can detect anomalous behavior patterns associated with Smart Install client functionality to provide early warning of potential exploitation attempts.