---
id: "CVE-2018-0172"
kind: "vulnerability"
aliases: ["CVE-2018-0172"]
title: "Cisco IOS and IOS XE Software: Cisco IOS and IOS XE Software Improper Input Validation Vulnerability"
severity: "high"
cvss: 8.6
epss: 0.0782
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Cisco IOS and IOS XE Software", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["cisco", "dhcp", "exploited", "infrastructure", "ios", "ios-xe", "network-gear"]
not_affected_if: ["no-dhcp-option-82", "non-cisco-hardware"]
published_at: "2018-03-28T22:29:01+00:00"
first_seen_at: "2026-10-23T19:11:52+00:00"
updated_at: "2026-10-23T21:57:35+00:00"
sources: [{"source": "kev", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2018-0172", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2018-0172", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2018-0172", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Cisco IOS and IOS XE Software: Cisco IOS and IOS XE Software Improper Input Validation Vulnerability

A flaw in how Cisco IOS and IOS XE handle DHCP option 82 encapsulation lets a crafted input crash the device, causing denial of service. CISA lists it as exploited in the wild.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:Cisco IOS and IOS XE Software affected ? fixed ?

## How to check

Run 'show version' on each Cisco IOS or IOS XE device and compare against the fixed release in the Cisco advisory; check whether DHCP relay or option 82 handling is configured.

## Fix

Apply the update from Cisco's security advisory for the affected IOS or IOS XE train, per CISA's required action.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2018-0172
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2018-0172
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2018-0172

## From the sources

A vulnerability in the DHCP option 82 encapsulation functionality of Cisco IOS Software and Cisco IOS XE Software could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a denial of service (DoS) condition. The vulnerability exists because the affected software performs incomplete input validation of option 82 information that it receives in DHCP Version 4 (DHCPv4) packets from DHCP relay agents. An attacker could exploit this vulnerability by sending a crafted DHCPv4 packet to an affected device. A successful exploit could allow the attacker to cause a heap overflow condition on the affected device, which will cause the device to reload and result in a DoS condition. Cisco Bug IDs: CSCvg62730.

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_Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai_