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5.3Medium

Cisco Ios Xe

CVE-2021-1236

Multiple Cisco products are affected by a vulnerability in the Snort application detection engine that could allow an unauthenticated, remote attacker to bypass the configured policies on an affected system. The vulnerability is due to a flaw in the detection algorithm. An attacker could exploit this vulnerability by sending crafted packets that would flow through an affected system. A successful exploit could allow the attacker to bypass the configured policies and deliver a malicious payload to the protected network.

What this means for your business

  • It affects Cisco Ios Xe. It matters if your company, or a supplier that handles your data, runs it.
  • An attacker can use it remotely, over a network, without a login, and without anyone at your company clicking anything.
  • FIRST's prediction model gives it a 2% chance of attack attempts being seen in the next 30 days, ranking above 81% of all known flaws.

What to do

  1. 1Check whether your company or your suppliers run Cisco Ios Xe, and which version. The affected versions are listed further down this page.
  2. 2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

Check if you’re exposedBook a call

Scoring

CVSS
5.3 (v3.1)
Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness
CWE-670
Assigned by
psirt@cisco.com

Dates

Published
2021-01-13
Last modified
2026-08-11
Sources
NVD

Affected products

  • Cisco Ios Xe- 17.4.1
  • Cisco 1100-4p Integrated Services Routerall versions
  • Cisco 1100-8p Integrated Services Routerall versions
  • Cisco 1101-4p Integrated Services Routerall versions
  • Cisco 1109-2p Integrated Services Routerall versions
  • Cisco 1109-4p Integrated Services Routerall versions
  • Cisco 1111x-8p Integrated Services Routerall versions
  • Cisco 4221 Integrated Services Routerall versions
  • Cisco 4321 Integrated Services Routerall versions
  • Cisco 4331 Integrated Services Routerall versions
  • Cisco 4351 Integrated Services Routerall versions
  • Cisco 4431 Integrated Services Routerall versions

As listed in the NVD configuration data. Not a statement about your estate.

References