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February 25, 2025
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How to Fix CVE-2018-0171: Critical Smart Install Vulnerability in Cisco IOS and IOS XE Software?
Cisco's Smart Install feature, found in IOS and IOS XE software, is a zero-touch deployment and configuration tool. However, a critical vulnerability, CVE-2018-0171, exists within this feature that could allow an unauthenticated remote attacker to trigger a device reload, leading to a denial-of-service (DoS) condition, or even execute arbitrary code. This article aims to equip security professionals with the knowledge and steps necessary to remediate this vulnerability effectively, minimizing the risk of exploitation. This article is for security professionals working in DevSecOps, application security, product security, vulnerability management and assessment, penetration testing and red teams, security operations and engineering teams.
A Short Introduction to Cisco Smart Install
Cisco Smart Install is a plug-and-play configuration and image-management feature that provides zero-touch deployment for new Cisco switches. It simplifies the process of setting up new network devices by allowing them to be pre-configured with a base image and configuration file, which are automatically applied when the device is connected to the network. This feature is particularly useful for large-scale deployments where manually configuring each switch would be time-consuming and error-prone. However, if not properly secured, Smart Install can become a significant security risk.
Summary of CVE-2018-0171
CVE ID: CVE-2018-0171
Description: A vulnerability in the Smart Install feature of Cisco IOS and 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, or to execute arbitrary code on an affected device.
CVSS Score: 9.8 (Critical)
CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
This vulnerability stems from improper validation of packet data within the Smart Install feature. An attacker could exploit this flaw by sending a specially crafted Smart Install message to a vulnerable device on TCP port 4786. Successful exploitation could lead to a buffer overflow, enabling the attacker to either crash the device (DoS) or execute arbitrary code, gaining control of the affected system. Due to the ease of exploitation and the high potential impact, this vulnerability is considered critical.
Impact of CVE-2018-0171
The impact of successfully exploiting CVE-2018-0171 can be severe. A remote, unauthenticated attacker could leverage this vulnerability to achieve several malicious outcomes:
Denial of Service (DoS): An attacker can trigger a reload of the affected device, causing network downtime and disruption of services.
Arbitrary Code Execution: The attacker could execute arbitrary code on the device, potentially gaining full control over the system. This could allow them to modify configurations, steal sensitive data, or use the compromised device as a launchpad for further attacks.
Indefinite Loop and Watchdog Crash: In some scenarios, the exploit could cause the device to enter an indefinite loop, ultimately leading to a watchdog crash, further exacerbating the DoS condition.
The high CVSS score (9.8) reflects the critical nature of this vulnerability, highlighting the potential for significant damage to confidentiality, integrity, and availability. For a better understanding of CVSS, it's important to understand its base metrics.
Products Affected by CVE-2018-0171
The CVE-2018-0171 vulnerability affects a wide range of Cisco devices running Cisco IOS and IOS XE Software with the Smart Install feature enabled. Due to the extensive list of affected products, it is imperative to consult Cisco's security advisory (cisco-sa-20180328-smi2) for a comprehensive list. However, the general categories of affected devices include:
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Product Category
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Affected Versions (General)
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|---|---|
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Cisco IOS Software
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Various versions
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Cisco IOS XE Software
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Various versions
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Cisco Catalyst Switches
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Various models
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|
Cisco Routers
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Various models
|
It is essential to note that devices not running IOS or IOS XE software, or those with the Smart Install feature explicitly disabled, are not affected by this vulnerability. Always refer to the official Cisco documentation for the most up-to-date and accurate information on affected products and versions. Cisco has released a security advisory detailing the affected products.
How to Check Your Product is Vulnerable?
Determining if your Cisco device is vulnerable to CVE-2018-0171 requires verifying whether the Smart Install feature is enabled and accessible. Here are several methods to check for vulnerability:
1. Check Smart Install Status:
Log in to the Cisco device's command-line interface (CLI) via SSH or console.
Enter privileged EXEC mode by typing
enableand providing the enable password.Use the command
show vstack configto check the Smart Install configuration.If Smart Install is enabled, the output will display the Smart Install configuration details. If the feature is disabled, the output will indicate that it is not configured.
2. Network Scan for TCP Port 4786:
Use a network scanning tool (e.g., Nmap) to scan your network for devices listening on TCP port 4786. This port is used by the Smart Install feature.
Any Cisco device responding on this port with Smart Install enabled is potentially vulnerable.
3. Banner Grabbing:
Use a tool like
telnetornetcatto connect to TCP port 4786 on a Cisco device.If the device responds with a Smart Install banner, it indicates that the feature is enabled and potentially vulnerable.
4. Configuration Review:
Review the device's configuration file for Smart Install-related commands.
Look for commands such as
vstack,smart-install, or configurations related to VLAN 1 (often used for Smart Install).
Important Considerations:
Even if Smart Install appears to be disabled, it is crucial to verify that it is completely disabled and not just inactive.
Ensure that your network segmentation and access control policies are properly configured to restrict access to TCP port 4786 from untrusted networks. Protecting your network involves various strategies, including zero trust security.
How to Fix CVE-2018-0171?
Addressing CVE-2018-0171 requires a multi-faceted approach, focusing on both immediate mitigation and long-term remediation. Here's a breakdown of the recommended steps:
1. Apply the Patch:
The primary remediation strategy is to apply the security patch provided by Cisco.
Visit the Cisco Security Advisory (cisco-sa-20180328-smi2) to identify the appropriate patch for your specific IOS or IOS XE software version and device model.
Download the patch from the Cisco Software Center and follow the installation instructions provided by Cisco.
After applying the patch, verify that the vulnerability is resolved by re-checking the Smart Install status and performing a network scan.
2. Disable Smart Install (If Not Required):
If the Smart Install feature is not essential for your network operations, the most effective mitigation is to disable it completely.
Log in to the Cisco device's CLI.
Enter privileged EXEC mode.
Use the command
no vstackto disable Smart Install.Save the configuration using the command
write memory.Verify that Smart Install is disabled by using the command
show vstack config.
3. Implement Access Control Lists (ACLs):
If disabling Smart Install is not feasible, restrict access to TCP port 4786 using ACLs.
Configure ACLs on your network devices (routers, firewalls) to allow access to TCP port 4786 only from trusted management networks.
Deny access to TCP port 4786 from all other networks, including the internet.
4. Network Segmentation:
Segment your network to isolate vulnerable devices from critical network resources.
Place the Cisco devices running Smart Install in a separate VLAN or network segment.
Implement strict access control policies to limit communication between this segment and other parts of the network.
5. Intrusion Detection/Prevention Systems (IDS/IPS):
Implement IDS/IPS rules to detect and block potential exploit attempts targeting CVE-2018-0171.
Configure your IDS/IPS to monitor network traffic for suspicious patterns, such as crafted Smart Install messages on TCP port 4786.
6. Monitor for Suspicious Activity:
Continuously monitor network traffic and device logs for any indications of exploitation attempts.
Look for unexpected device reloads, unusual network traffic on port 4786, and any unauthorized configuration changes. Monitoring essential files and directories can provide valuable insights.
By implementing these remediation steps, you can significantly reduce the risk posed by CVE-2018-0171 and protect your network from potential attacks. Remember to prioritize patching and disabling the Smart Install feature whenever possible, as these are the most effective ways to address this critical vulnerability.
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Arun KL
Arun KL is a cybersecurity professional with 15+ years of experience in IT infrastructure, cloud security, vulnerability management, Penetration Testing, security operations, and incident response. He is adept at designing and implementing robust security solutions to safeguard systems and data. Arun holds multiple industry certifications including CCNA, CCNA Security, RHCE, CEH, and AWS Security.
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