CVE-2021-1389

Cisco IOS XR and Cisco NX-OS Software IPv6 Access Control List Bypass Vulnerability

MEDIUM

6.5

CVSS Score

Published: February 4, 2021 at 04:40 PM UTC

Updated: June 17, 2026 at 03:31 AM UTC

12 products affected across 1 vendorNx OSIOS XrNexus 3600

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Severity

MEDIUM6.5

Exploit prediction

EPSS 1%

SSVC

No known exploit

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

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

IOS Xr · Cisco

95%

v < 6.6.37.1.0 7.2.0

Affected range stops below 6.6.3, so it looks safe — our inference, not a vendor statement

cisco-ncs-540 (environment) · cisco-ncs-5501 (environment) · cisco-ncs-5501-se (environment) · cisco-ncs-5502 (environment) · cisco-ncs-5502-se (environment) · cisco-ncs-5508 (environment) · cisco-ncs-5516 (environment) · cisco-ncs-560 (environment)

Nx OS · Cisconpm

95%

All versions

cisco-nexus-3600 (environment) · cisco-nexus-9500-r (environment)

Ncs 540 · Ciscodevice

80%

All versions

Ncs 5501 · Ciscodevice

80%

All versions

Ncs 5501-Se · Ciscodevice

80%