CVE-2021-34767

What it is

A vulnerability in IPv6 traffic processing of Cisco IOS XE Wireless Controller Software for Cisco Catalyst 9000 Family Wireless Controllers could allow an unauthenticated, adjacent attacker to cause a Layer 2 (L2) loop in a configured VLAN, resulting in a denial of service (DoS) condition for that VLAN. The vulnerability is due to a logic error when processing specific link-local IPv6 traffic. An attacker could exploit this vulnerability by sending a crafted IPv6 packet that would flow inbound through the wired interface of an affected device. A successful exploit could allow the attacker to cause traffic drops in the affected VLAN, thus triggering the DoS condition.

At a glance

Exploitability

Can be exploited from the same network segment without logging in. High risk of service disruption.

Exploit odds

0.8% chance of exploitation in the next 30 days (EPSS).

Fix

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

Timeline

1. 2021-09-23 03:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2. 2026-06-17 03:56 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.8% in the next 30 days (EPSS).
• Severity: 7.4 HIGH (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2021-09-23 03:15 UTC

Last modified

2026-06-17 03:56 UTC

Exploit probability

0.8% · EPSS, next 30 days

Weakness

CWE-670

Record status

Analyzed

Affected

• Cisco iOS Xe
• Cisco iOS Xe 3.15.1xbs
• Cisco iOS Xe 3.15.2xbs
• Cisco iOS Xe 16.7.1
• Cisco iOS Xe 16.7.1a
• Cisco iOS Xe 16.7.1b
• Cisco iOS Xe 16.7.2
• Cisco iOS Xe 16.7.3

Attack profile CVSS 3.1 · 7.4

Attack vector

Adjacent network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

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-2021-34767.md and follow it. Check whether this project is affected by CVE-2021-34767. 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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