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Actively exploited in the wild. This CVE is on the CISA Known Exploited Vulnerabilities list — treat remediation as urgent. Federal remediation due by 3 May 2022.
iOSOperating system · Cisco

CVE-2018-0171

CRITICAL · 9.8 CVSS v3.1 Published 2018-03-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
In the wild High EPSS Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

A buffer overflow vulnerability in Cisco IOS/IOS XE Smart Install feature allows remote, unauthenticated attackers to send crafted packets on TCP port 4786, potentially causing device reload (DoS), arbitrary code execution, or a watchdog crash due to an indefinite loop.

MitigationDisable the Smart Install feature on affected devices or block TCP port 4786 at network boundaries; apply Cisco patches when available.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
iOSOperating system
Affected:= 15.2\(5\)e

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Identify the Cisco iOS version
    Execute 'show version' on the device CLI and locate the version string in the output (e.g., 'Version 15.2(5)E')
    Affected if The version shown is exactly 15.2(5)e (case-insensitive match)
  2. Confirm Smart Install feature is enabled
    Execute 'show vstack' or check the running configuration with 'show running-config | include vstack|smart-install' to see if Smart Install is actively configured
    Affected if Smart Install is listed as enabled or the feature appears in the running configuration
  3. Verify TCP port 4786 is accessible
    Execute 'show control-plane host open-ports' or use 'show ip socket' to determine if port 4786 is listening and open on the device
    Affected if Port 4786 is shown as open and listening on the device

The device is affected if it runs iOS version 15.2(5)e with Smart Install feature enabled and TCP port 4786 is accessible.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Disable the Smart Install feature on affected devices or block TCP port 4786 at network boundaries; apply Cisco patches when available.

Recommended fix High confidence

Cisco IOS version 15.2(4)E5 or later in the E train, or 15.3(1)T1 or later in the T train (or equivalent fixed version in other trains). Consult Cisco's official bug details for your specific hardware platform.

  1. 1. Verify the Smart Install feature status on the device by running 'show vstack' or 'show run | include vstack' in privileged EXEC mode.
  2. 2. If Smart Install is enabled, disable it using the configuration command 'no vstack' in global configuration mode.
  3. 3. Alternatively or additionally, upgrade the Cisco IOS or IOS XE software to a fixed release that addresses CVE-2018-0171. Cisco fixed this vulnerability in multiple version trains including the E train (15.2(4)E5 and later) and T train (15.3(1)T1 and later).
  4. 4. After upgrading, verify the Smart Install feature is disabled and the new IOS version is running with 'show version'.
  5. 5. Block TCP port 4786 at network perimeter devices (firewalls/ACLs) as an additional defense-in-depth measure.
Caveat Ensure compatibility between the new IOS version and your hardware platform; some legacy platforms may not support newer IOS trains.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in iOS Exploited in the wild — priority engagement
  • Consultation3.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA2.0 h
12.0 hours of engineering $2,130
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2018-0171 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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  • No spam, self-promotion, credentials, or personal data