Cisco IOS and IOS XE Smart Install Remote Code Execution and DoS Vulnerability (CVE-2018-0171) Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTCisco network switches and routers running Cisco IOS and IOS XE Software with the Smart Install client feature enabled.
Unauthenticated, remote attackers can send crafted packets to TCP port 4786, triggering a heap-based buffer overflow that leads to device reload (DoS) or arbitrary code execution (RCE) with elevated privileges.
Disable the Smart Install feature using the 'no vstack' command, or restrict access to TCP port 4786 using Infrastructure Access Control Lists (ACLs) if the feature is required.
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Cisco has released software updates that address this vulnerability. Administrators should identify their current version and upgrade to a patched release using the following procedure:
# Verify current IOS version and check if TCP port 4786 is active
show version
show tcp brief | include 4786
# Download the patched image from your TFTP server and set the boot variable
copy tftp: flash:
# (Enter server IP and filename, e.g., c2960x-universalk9-mz.152-7.E.bin)
configure terminal
no boot system
boot system flash:/c2960x-universalk9-mz.152-7.E.bin
exit
write memory
reload2. Temporary Workaround & Hardening Configuration
If you do not actively use the Smart Install feature, disable it immediately. If the feature must remain active, implement an Infrastructure ACL to restrict access to TCP port 4786 to authorized Smart Install Directors only.
# 1. Disable Smart Install completely (Highly Recommended)
configure terminal
no vstack
exit
write memory
# 2. If disabling is not possible, restrict TCP port 4786 to a trusted Director IP (e.g., 10.1.1.50)
configure terminal
ip access-list extended RESTRICT_SMI
permit tcp host 10.1.1.50 any eq 4786
deny tcp any any eq 4786
permit ip any any
exit
# Apply the ACL to the external-facing interface
interface GigabitEthernet0/1
ip access-group RESTRICT_SMI in
exit
write memory3. Log Audit & IoC Verification Commands
Inspect the device for active connections on the Smart Install port and review system logs for unexpected reboots or crash signatures.
# Check for active sockets or connections on TCP port 4786
show sockets | include 4786
show tcp brief all | include 4786
# Search system logs for Smart Install activity or unexpected reload events
show logging | include SMI|SmartInstall|STACK|Command
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2018-0171) is a critical heap-based buffer overflow vulnerability in the Smart Install feature of Cisco IOS and IOS XE Software. Smart Install is a plug-and-play technology designed to automate the initial configuration and image loading for new switches. The root cause of this vulnerability lies in the improper validation of input packet data size within the Smart Install message parser. When a crafted packet is processed, the lack of boundary validation allows an attacker to overwrite adjacent memory blocks.
2. Exploitation Mechanics & Attack Scenario
The Smart Install client operates by listening on TCP port 4786. An attacker can scan for target devices exposing this port and transmit a specially crafted Smart Install protocol message. Because the software fails to validate the length of the incoming data before copying it into an internal buffer, the payload overflows the allocated memory space. This corruption can either trigger an infinite loop leading to a watchdog crash and device reload (Denial of Service), or allow the attacker to hijack the execution flow to run arbitrary code with full system privileges.
3. Infrastructure & Business Impact
With a CVSS score of 9.8 (Critical) and its inclusion in the CISA KEV catalog, this vulnerability represents an extreme risk to enterprise infrastructure. Successful exploitation grants the attacker complete control over core network switches and routers. This can lead to total network compromise, traffic interception, man-in-the-middle (MitM) attacks, lateral movement into internal segments, and severe operational downtime.
Official Vendor Advisories & References
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, or to execute arbitrary code on an affected device. The vulnerability is due to improper validation of packet data. An attacker could exploit this vulnerability by sending a crafted Smart Install message to an affected device on TCP port 4786. A successful exploit could allow the attacker to cause a buffer overflow on the affected device, which could have the following impacts: Triggering a reload of the device, Allowing the attacker to execute arbitrary code on the device, Causing an indefinite loop on the affected device that triggers a watchdog crash. Cisco Bug IDs: CSCvg76186.
Frequently Asked SecOps Questions (CVE-2018-0171)
FAQQ1. How critical is CVE-2018-0171 and is it actively exploited in the wild?
CVE-2018-0171 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 99.5%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2018-0171?
Primary impacted vendors include cisco across ios, ios_xe. Scope summary: All Cisco devices running Cisco IOS or IOS XE Software that have the Smart Install client feature enabled and are listening on TCP port 4786.
Q3. What temporary mitigations or workarounds exist for CVE-2018-0171 before patching?
[Mitigation] Disable the Smart Install feature using the 'no vstack' command, or restrict access to TCP port 4786 using Infrastructure Access Control Lists (ACLs) if the feature is required. Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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