CVE-2021-1394

What it is

A vulnerability in the ingress traffic manager of Cisco IOS XE Software for Cisco Network Convergence System (NCS) 520 Routers could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition in the web management interface of an affected device. This vulnerability is due to incorrect processing of certain IPv4 TCP traffic that is destined to an affected device. An attacker could exploit this vulnerability by sending a large number of crafted TCP packets to the affected device. A successful exploit could allow the attacker to cause the web management interface to become unavailable, resulting in a DoS condition. Note: This vulnerability does not impact traffic that is going through the device or going to the Management Ethernet interface of the device.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

1.3% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-03-24 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:31 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 1.3% in the next 30 days (EPSS).
• Severity: 5.3 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-03-24 20:15 UTC

Last modified

2026-06-17 03:31 UTC

Exploit probability

1.3% · EPSS, next 30 days

Weakness

CWE-399

Record status

Modified

Affected

• Cisco iOS Xe 16.10.1
• Cisco iOS Xe 16.10.1a
• Cisco iOS Xe 16.10.1b
• Cisco iOS Xe 16.10.1c
• Cisco iOS Xe 16.10.1d
• Cisco iOS Xe 16.10.1e
• Cisco iOS Xe 16.10.1f
• Cisco iOS Xe 16.10.1g

Attack profile CVSS 3.1 · 5.3

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

None

Integrity

None

Availability

Low

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-1394.md and follow it. Check whether this project is affected by CVE-2021-1394. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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