---
id: CVE-1999-1306
title: >-
  Cisco IOS 9.1 and earlier does not properly handle extended IP access lists
  when the IP route cache is enabled and the "established" keyword is set, which
  could allow attackers to bypass filters.
summary: >-
  Cisco IOS 9.1 and earlier does not properly handle extended IP access lists
  when the IP route cache is enabled and the "established" keyword is set, which
  could allow attackers to bypass filters.
severity: high
cvss: 7.5
cvssVector: 'AV:N/AC:L/Au:N/C:P/I:P/A:P'
published: '1992-12-10'
updated: '2026-06-16'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-1999-1306'
references:
  - url: 'http://www.cert.org/advisories/CA-1992-20.html'
    label: cve@mitre.org
  - url: 'http://www.cert.org/advisories/CA-1992-20.html'
    label: af854a3a-2127-422b-91ae-364da2661108
tags:
  - nvd
epss: 0.01394
epssPercentile: 0.70759
ingestedAt: '2026-06-19T03:39:00.709Z'
---

## Overview

Cisco IOS 9.1 and earlier does not properly handle extended IP access lists when the IP route cache is enabled and the "established" keyword is set, which could allow attackers to bypass filters.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.