Cloudanix VulnDB

CVE-2018-0156

High · 7.5 CISA KEV

CVSS

7.5

EPSS

9.4%

Published

Mar 28, 2018

CISA due date

Mar 17, 2022

Cloudanix analysis

Act now SSVC: Attend

A flaw in certain Cisco network devices lets anyone on the network send a specially made message that makes the device restart, knocking it offline until it comes back up.

Active In The Wild
Exploitation
Remote Unauthenticated
Attacker needs
None
Complexity
Trivial
Impact
Denial Of Service
Component
Network Service
Class
Improper Input Validation
Remediation
Upgrade
Effort
Medium
Patch risk
Medium

What it actually does

The flaw stems from improper validation of packet data in the Smart Install feature, allowing an unauthenticated remote attacker to send a crafted packet on TCP port 4786 that triggers an immediate device reload on affected client switches.

Why it matters to the business

Causes repeated denial-of-service outages on network infrastructure devices, disrupting operations; listed in CISA KEV with a 2022 remediation deadline that has passed, increasing urgency for any remaining unpatched Cisco IOS and IOS XE deployments.

How an attack unfolds

An attacker identifies exposed Smart Install client devices and transmits a single specially crafted packet to TCP port 4786; the lack of input validation causes the device to reload, resulting in immediate loss of availability. Active exploitation has been observed in the wild.

How to fix it

Apply the fixed software versions provided by Cisco for the affected IOS and IOS XE releases; disable the Smart Install feature on client switches when not required; monitor for the CISA KEV due date compliance.

How to confirm the fix worked

Verify that devices no longer accept or process the malicious Smart Install packets on TCP 4786 after upgrade; confirm configuration changes disable the feature where possible and test reload behavior under simulated traffic.

Typical attack path

  1. Scan for Cisco IOS/IOS XE devices listening on TCP 4786 with Smart Install client configuration
  2. Craft a malicious packet that bypasses input validation checks
  3. Transmit the packet remotely without authentication or user interaction
  4. Trigger device reload and confirm resulting denial of service

How to detect it

Review firewall, IDS, and device logs for inbound connections or packets targeting TCP port 4786 from untrusted sources; look for sudden device reloads or crash logs coinciding with traffic on that port; correlate with threat actor activity noted for this vulnerability.

  • inbound TCP 4786
  • crafted Smart Install packet
  • device reload after TCP 4786 traffic

What your security team should do

  • Prioritize patching of all KEV-listed Cisco devices before any other work
  • Disable Smart Install client functionality on switches that do not require it
  • Implement network segmentation and ACLs to restrict access to TCP 4786
  • Monitor EPSS trend and threat intelligence feeds for continued active exploitation

The record

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.

Affected packages

Ecosystem Package Introduced Fixed

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