---
id: "CVE-2018-0173"
kind: "vulnerability"
aliases: ["CVE-2018-0173"]
title: "Cisco IOS and IOS XE Software: Cisco IOS and IOS XE Software Improper Input Validation Vulnerability"
severity: "high"
cvss: 8.6
epss: 0.07608
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-relay-option-82", "non-cisco-network"]
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-2018-0173", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2018-0173", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2018-0173", "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

Cisco IOS and IOS XE routers and switches mishandle DHCPv4 packets carrying encapsulated option 82 data during restoration. An attacker can crash or reload the device, causing denial of service.

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

## Affected

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

## Fix

Apply the Cisco IOS and IOS XE updates per vendor instructions (CISA KEV required action). Fixed versions: unknown from sources.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2018-0173
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2018-0173
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2018-0173

## From the sources

A vulnerability in the Cisco IOS Software and Cisco IOS XE Software function that restores encapsulated option 82 information in DHCP Version 4 (DHCPv4) packets could allow an unauthenticated, remote attacker to cause an affected device to reload, resulting in a Relay Reply denial of service (DoS) condition. The vulnerability exists because the affected software performs incomplete input validation of encapsulated option 82 information that it receives in DHCPOFFER messages from DHCPv4 servers. An attacker could exploit this vulnerability by sending a crafted DHCPv4 packet to an affected device, which the device would then forward to a DHCPv4 server. When the affected software processes the option 82 information that is encapsulated in the response from the server, an error could occur. A successful exploit could allow the attacker to cause the affected device to reload, resulting in a DoS condition. Cisco Bug IDs: CSCvg62754.

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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_