Cisco Nexus 9000 Series Fabric Switches in ACI Mode Endpoint Group Contract Bypass Vulnerability

Description

A vulnerability in the endpoint group (EPG) contract functionality of Cisco Nexus 9000 Series Fabric Switches in ACI Mode could allow an unauthenticated, remote attacker to bypass configured EPG contracts. This vulnerability is due to an improper control with EPG contracts. An attacker could exploit this vulnerability by sending IPv4 or IPv6 packets using UDP source and destination ports that are assigned to DHCP traffic through an affected device. A successful exploit could allow the attacker to bypass EPG contracts on the affected device. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-aci-epgcbp-SfDU7NLf This advisory is part of a group of advisories. For a complete list of the advisories and links to them, see Cisco Advance Notification for Publication of October 7, 2026, Security Advisories . In addition, for further documentation of improvements and fixes in Cisco NX-OS Software, see Cisco NX-OS Software Security Hardening Release: October 2026 . Security Impact Rating: Medium CVE: CVE-2026-20038

What to do

Install the fixed versions listed in the official advisory. If you cannot update right away, apply the workarounds or mitigations it describes and limit access to the affected service.

Details

Vendor

Cisco

Product

Cisco Nexus 9000 Series (ACI Mode)

CVE

CVE-2026-20038

Affected versions

Cisco NX-OS System Software in ACI Mode 15.2: 25 versions, from 15.2(1g) to 15.2(8i)
Cisco NX-OS System Software in ACI Mode 16.0: 20 versions, from 16.0(1g) to 16.0(9f)
Cisco NX-OS System Software in ACI Mode 15.3: 7 versions, from 15.3(1d) to 15.3(2f)
Cisco NX-OS System Software in ACI Mode 16.1: 7 versions, from 16.1(1f) to 16.1(5e)
Cisco NX-OS System Software in ACI Mode 16.2: 16.2(1g); 16.2(2e) (from the advisory and NVD; check the exact builds in the official advisory)

CVSS score

5.8

Actively exploited

Not known at this time

Source

Cisco PSIRT – original advisory

Published

October 7, 2026

The description and the recommended action are quoted from the public advisory (the action is our generic advice); severity, exploitation status and affected versions are compiled automatically from public sources and may contain errors. The vendor's original advisory prevails: check it before taking action. This information is provided without warranty and does not replace a professional assessment.