CVE-2021-20267Network attack vector

Traffic interception via permissive IPv6 anti-spoofing rules

Published May 28, 2021 · Updated Aug 3, 2024

Anti-spoofing bypass in affected OpenStack Neutron releases allows guest OS users to impersonate IPv6 addresses on OVS networks. The OVS firewall accepts IPv6 Neighbor Advertisement and DHCPv6 traffic without restricting both source IP and MAC addresses to the port's assignments. Exploitation requires control of an instance attached to the virtual switch and permits traffic interception or service interruption for spoofed addresses.

CVSS severity7.1
High
EPSS probability1.02%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Anti-spoofing bypass in affected OpenStack Neutron releases allows guest OS users to impersonate IPv6 addresses on OVS networks. The OVS firewall accepts IPv6 Neighbor Advertisement and DHCPv6 traffic without restricting both source IP and MAC addresses to the port's assignments. Exploitation requires control of an instance attached to the virtual switch and permits traffic interception or service interruption for spoofed addresses.

The record

CVE
CVE-2021-20267
Published
May 28, 2021
Updated
Aug 3, 2024
Vendor
OpenStack
Product
Neutron
Classifications
CWE-345, T1557
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=openstack-neutron 15.3.3, openstack-neutron 16.3.1, openstack-neutron 17.1.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

OpenStack · Neutronversion=openstack-neutron 15.3.3, openstack-neutron 16.3.1, openstack-neutron 17.1.1

Published CVSS scores

5.5NIST NVDAV:N/AC:L/Au:S/C:P/I:N/A:P
7.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-345Insufficient Verification of Data Authenticity
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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