CVE-2021-1389: Cisco IOS XR and Cisco NX-OS Software IPv6 Access Control List Bypass Vulnerability

Severity: medium (CVSS 6.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.2% 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-284

Description

A vulnerability in the IPv6 traffic processing of Cisco IOS XR Software and Cisco NX-OS Software for certain Cisco devices could allow an unauthenticated, remote attacker to bypass an IPv6 access control list (ACL) that is configured for an interface of an affected device. The vulnerability is due to improper processing of IPv6 traffic that is sent through an affected device. An attacker could exploit this vulnerability by sending crafted IPv6 packets that traverse the affected device. A successful exploit could allow the attacker to access resources that would typically be protected by the interface ACL.

Affected products

Cisco IOS XR Software: before 6.6.3; 7.1.0, 7.2.0 — fixed in 6.6.3
Cisco NX-OS: all versions

How to fix

Upgrade to a fixed version: Cisco IOS XR Software 6.6.3. Check the vendor advisory for mitigations.

References

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