CVE-2021-1268: Cisco IOS XR Software IPv6 Flood Denial of Service Vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-02-04 · updated 2026-06-17
Weakness: CWE-1076

Description

A vulnerability in the IPv6 protocol handling of the management interfaces of Cisco IOS XR Software could allow an unauthenticated, adjacent attacker to cause an IPv6 flood on the management interface network of an affected device. The vulnerability exists because the software incorrectly forwards IPv6 packets that have an IPv6 node-local multicast group address destination and are received on the management interfaces. An attacker could exploit this vulnerability by connecting to the same network as the management interfaces and injecting IPv6 packets that have an IPv6 node-local multicast group address destination. A successful exploit could allow the attacker to cause an IPv6 flood on the corresponding network. Depending on the number of Cisco IOS XR Software nodes on that network segment, exploitation could cause excessive network traffic, resulting in network degradation or a denial of service (DoS) condition.

Affected products

Cisco IOS XR Software: before 6.7.3; from 7.1.0 before 7.1.3; from 7.2.0 before 7.2.2; 7.3.0 — fixed in 6.7.3, 7.1.3, 7.2.2

How to fix

Upgrade to a fixed version: Cisco IOS XR Software 6.7.3, 7.1.3, 7.2.2. Check the vendor advisory for mitigations.

References

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