---
id: "CVE-2017-12231"
kind: "vulnerability"
aliases: ["CVE-2017-12231"]
title: "Cisco IOS software: Cisco IOS Software Network Address Translation Denial-of-Service Vulnerability"
severity: "high"
cvss: 7.8
epss: 0.0707
exploited: true
status: "open"
category: "infrastructure"
products: [{"name": "Cisco IOS software", "fixed": [], "affected": "", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["cisco-ios", "exploited", "infrastructure", "network-edge", "routers"]
not_affected_if: ["nat-not-configured", "patched-ios-release"]
published_at: "2017-09-29T01:34:48+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-2017-12231", "first_seen_at": "2026-10-23T19:11:52+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2017-12231", "first_seen_at": "2026-10-23T19:13:44+00:00"}, {"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2017-12231", "first_seen_at": "2026-10-23T21:57:35+00:00"}]
---

# Cisco IOS software: Cisco IOS Software Network Address Translation Denial-of-Service Vulnerability

Cisco IOS software has a flaw in its Network Address Translation code that lets an unauthenticated remote attacker crash or hang the device. The attacker gets denial of service, not code execution, and CISA lists it as actively exploited.

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

## Affected

- vendor:Cisco IOS software affected ? fixed ?

## How to check

Run 'show version' on each Cisco IOS device and compare against the fixed release in the Cisco advisory; check whether NAT is configured with 'show running-config | include ip nat'.

## Fix

Upgrade Cisco IOS to a fixed release per the vendor advisory; the sources do not name the fixed version.

## Timeline

- 2026-10-23T19:11:52+00:00 kev https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2017-12231
- 2026-10-23T19:13:44+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2017-12231
- 2026-10-23T21:57:35+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2017-12231

## From the sources

A vulnerability in the implementation of Network Address Translation (NAT) functionality in Cisco IOS 12.4 through 15.6 could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. The vulnerability is due to the improper translation of H.323 messages that use the Registration, Admission, and Status (RAS) protocol and are sent to an affected device via IPv4 packets. An attacker could exploit this vulnerability by sending a crafted H.323 RAS packet through an affected device. A successful exploit could allow the attacker to cause the affected device to crash and reload, resulting in a DoS condition. This vulnerability affects Cisco devices that are configured to use an application layer gateway with NAT (NAT ALG) for H.323 RAS messages. By default, a NAT ALG is enabled for H.323 RAS messages. Cisco Bug IDs: CSCvc57217.

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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_