No exploitation reportedFix available

CVE-2021-20267

Q: Is CVE-2021-20267 actively exploited?

Active exploitation of CVE-2021-20267 has not been confirmed. Its EPSS score was 1.0% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-20267?

CVE-2021-20267 has a CVSS v3 base score of 7.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-05-28
WeaknessCWE-345

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC

2021-05-2819:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-20267?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-20267?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Redhat openstack platform

Branch	Affected	Fixed in	Source
10.0	= 10.0	no fix published	NVD
13.0	= 13.0	no fix published	NVD
16.1	= 16.1	no fix published	NVD
16.2	= 16.2	no fix published	NVD

Openstack neutron

Branch	Affected	Fixed in	Source
17.x	≥ 17.0.0, < 17.1.3	17.1.3	NVD
16.3	< 16.3.3	16.3.3	NVD
18.0	= 18.0.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Advisories and patches

bugzilla.redhat.comPatch
security.openstack.orgPatch · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.1read 2026-10-23
NVDCVSS 2.05.5read 2026-10-23
CNAweakness (CWE)CWE-345read 2026-10-23
FIRST EPSSEPSS score1.0 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H
Published: 2021-05-28
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-20267?

Is CVE-2021-20267 actively exploited?

Active exploitation of CVE-2021-20267 has not been confirmed. Its EPSS score was 1.0% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-20267?

CVE-2021-20267 has a CVSS v3 base score of 7.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H.

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