---
id: "CVE-2017-12240"
kind: "vulnerability"
aliases: ["CVE-2017-12240"]
title: "Cisco IOS and IOS XE Software: Cisco IOS and IOS XE Software DHCP Remote Code Execution Vulnerability"
severity: "critical"
cvss: 10.0
epss: 0.13773
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Cisco IOS and IOS XE Software", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["cisco", "exploited", "infrastructure", "ios", "ios-xe", "network-gear"]
not_affected_if: ["no-dhcp-relay-configured"]
published_at: "2017-09-29T01:34:49+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-2017-12240", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2017-12240", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2017-12240", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Cisco IOS and IOS XE Software: Cisco IOS and IOS XE Software DHCP Remote Code Execution Vulnerability

Cisco IOS and IOS XE DHCP relay subsystem contains a flaw that lets an unauthenticated remote attacker execute arbitrary code on the device. A successful attacker gains full control of the affected router or switch.

_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 the device to identify the IOS or IOS XE release, then compare it against the fixed releases in the Cisco advisory.

## Fix

Upgrade IOS or IOS XE to a fixed release per the Cisco security advisory; the CISA entry says only to apply vendor updates.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2017-12240
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2017-12240
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2017-12240

## From the sources

The DHCP relay subsystem of Cisco IOS 12.2 through 15.6 and Cisco IOS XE Software contains a vulnerability that could allow an unauthenticated, remote attacker to execute arbitrary code and gain full control of an affected system. The attacker could also cause an affected system to reload, resulting in a denial of service (DoS) condition. The vulnerability is due to a buffer overflow condition in the DHCP relay subsystem of the affected software. An attacker could exploit this vulnerability by sending a crafted DHCP Version 4 (DHCPv4) packet to an affected system. A successful exploit could allow the attacker to execute arbitrary code and gain full control of the affected system or cause the affected system to reload, resulting in a DoS condition. Cisco Bug IDs: CSCsm45390, CSCuw77959.

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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_