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Fencer Vulns
high 7.1

CVE-2021-20267 json

Openstack Neutron has Insufficient Verification of IPv6 addresses

published 2021-05-28 5 y ago modified 2026-06-17 4 mo ago also GHSA-w8hx-f868-pvch , PYSEC-2021-136 , EUVD-2021-0142

cvss
7.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 64%
public exploits
0
none known

Summary

A flaw was found in openstack-neutron's default Open vSwitch firewall rules. By sending carefully crafted packets, anyone in control of a server instance connected to the virtual switch can impersonate the IPv6 addresses of other systems on the network, resulting in denial of service or in some cases possibly interception of traffic intended for other destinations. Only deployments using the Open vSwitch driver are affected. Source: OpenStack project. Versions before openstack-neutron 15.3.3, openstack-neutron 16.3.1 and openstack-neutron 17.1.1 are affected.

Patch / fix

  • pypi neutron 15.3.3, 16.3.1, 17.1.1
  • openstack neutron 16.3.3, 17.1.3
  • neutron Debian 14, Debian 13, Debian 12 2:17.1.1-5

debian advisories DEBIAN-CVE-2021-20267

  • neutron Ubuntu 18.04 LTS 2:12.1.1-0ubuntu8.1
  • neutron Ubuntu 20.04 LTS 2:16.4.2-0ubuntu6.2

ubuntu advisories UBUNTU-CVE-2021-20267

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-20267 updated cvss 7.1

openstack-neutron: Anti-spoofing bypass using Open vSwitch

  • Red Hat OpenStack Platform 10 (Newton) python-neutron, openstack-neutron, python-neutron-tests, openstack-neutron-ml2, openstack-neutron-common, openstack-neutron-rpc-server, +5 more Red Hat OpenStack Platform 13 (Queens) python-neutron, openstack-neutron, openstack-neutron-ml2, openstack-neutron-common, openstack-neutron-rpc-server, openstack-neutron-linuxbridge, +4 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat OpenStack Platform 16.1 python3-neutron, openstack-neutron, openstack-neutron-ml2, openstack-neutron-common, openstack-neutron-rpc-server, openstack-neutron-linuxbridge, +4 more
    affected: workaround, no fix available “Fix deferred”
  • Red Hat OpenStack Platform 16.2 python3-neutron, openstack-neutron, openstack-neutron-ml2, openstack-neutron-common, openstack-neutron-rpc-server, openstack-neutron-linuxbridge, +4 more Red Hat OpenStack Platform 17.1 python3-neutron, openstack-neutron, openstack-neutron-ml2, openstack-neutron-common, openstack-neutron-rpc-server, openstack-neutron-linuxbridge, +6 more
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat OpenStack Platform 18.0 openstack-neutron
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

1.04% chance of exploitation in the next 30 days, higher than 64% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
NVD 2.0 5.5 AV:N/AC:L/Au:S/C:P/I:N/A:P
GitHub 3.1 7.1 CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H

Affected packages

ecosystem package affected fixed in
pypi neutron
>=16.0.0, <16.3.1
<15.3.3
>=17.0.0, <17.1.1
16.3.1
15.3.3
17.1.1

Affected products

  • n/a openstack-neutron

Classification

Weakness
  • CWE-345 Insufficient Verification of Data Authenticity

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.