How severe is CVE-2021-20267?

CVE-2021-20267 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability high.

Is CVE-2021-20267 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (59th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-20267?

CVE-2021-20267 primarily affects Redhat Openstack Platform. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2021-20267?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-20267 published?

CVE-2021-20267 was published on 2021-05-28 and last updated on 2026-06-17.

CVE-2021-20267

CVE-2021-20267 is a high-severity vulnerability in Redhat Openstack Platform with a CVSS 3.x base score of 7.1. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-345.

Key facts

Severity: High (CVSS 3.x base score 7.1)
CVSS v2: 5.5
EPSS exploit prediction: 1% (59th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-345
Affected product: Redhat Openstack Platform
Published: 2021-05-28
Last modified: 2026-06-17

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.

Frequently asked questions

What is CVE-2021-20267?: 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.
How severe is CVE-2021-20267?: CVE-2021-20267 has a CVSS 3.x base score of 7.1, rated high severity. It is exploitable over network with low attack complexity, requires low privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability high.
Is CVE-2021-20267 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (59th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-20267?: CVE-2021-20267 primarily affects Redhat Openstack Platform. In total, 6 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2021-20267?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-20267 published?: CVE-2021-20267 was published on 2021-05-28 and last updated on 2026-06-17.

References

Affected products (6)

cpe:2.3:a:openstack:neutron:*:*:*:*:*:*:*:*
cpe:2.3:a:openstack:neutron:18.0.0:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openstack_platform:10.0:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openstack_platform:13.0:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openstack_platform:16.1:*:*:*:*:*:*:*
cpe:2.3:a:redhat:openstack_platform:16.2:*:*:*:*:*:*:*

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