CVE-2021-20267 [High] | Denial of Service in Neutron

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.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.13%	1.01%	+0.89%
2	2026-05-15	0.19%	0.13%	-0.06%
3	2026-05-12	—	0.19%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.13%

1.01%

+0.89%

2026-05-15

0.19%

0.13%

-0.06%

2026-05-12

—

0.19%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
7.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:L) Some sensitive info could get out, but not a total data dump. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.8	4.2	[email protected]
5.5	2.0	MEDIUM	`AV:N/AC:L/Au:S/C:P/I:N/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:L) Exploitation conditions are straightforward and predictable. Authentication (AU:S) A single authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:N) No integrity impact. Availability impact (A:P) Partial availability impact.	8.0	4.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

7.1

3.1

HIGH

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:H Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:L): Some sensitive info could get out, but not a total data dump.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.8

4.2

[email protected]

5.5

2.0

MEDIUM

AV:N/AC:L/Au:S/C:P/I:N/A:P Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:L): Exploitation conditions are straightforward and predictable.
Authentication (AU:S): A single authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:N): No integrity impact.
Availability impact (A:P): Partial availability impact.

8.0

4.9

[email protected]

OS Trackers for CVE-2021-20267

vendor	priority	summary	link
`debian`	not yet assigned	CVE-2021-20267 not yet assigned priority: Debian including 1 source packages (neutron), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-20267
`redhat`	medium	—	https://access.redhat.com/security/cve/CVE-2021-20267
`suse`	high	CVE-2021-20267 severity important: SUSE including 11 source package names (openstack-neutron, openstack-neutron-dhcp-agent, …), 55 product×package rows across 5 product lines (HPE Helion OpenStack 8, SUSE OpenStack Cloud 8, … (5 product lines)): Known Not Affected 55.	https://www.suse.com/security/cve/CVE-2021-20267/
`ubuntu`	medium	CVE-2021-20267 medium priority: Ubuntu including 1 source packages (neutron), 16 status rows across 16 suites (bionic, focal, groovy, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 9, released 3, ignored 2, DNE 1, needed 1.	https://ubuntu.com/security/CVE-2021-20267

Affected software / configurations for CVE-2021-20267

Vendor	Product	Version	Raw CPE
openstack	neutron	< 16.3.3	cpe:2.3:a:openstack:neutron::::::::
openstack	neutron	>= 17.0.0, < 17.1.3	cpe:2.3:a:openstack:neutron::::::::
openstack	neutron	18.0.0	cpe:2.3:a:openstack:neutron:18.0.0:::::::*
redhat	openstack_platform	10.0	cpe:2.3:a:redhat:openstack_platform:10.0:::::::*
redhat	openstack_platform	13.0	cpe:2.3:a:redhat:openstack_platform:13.0:::::::*
redhat	openstack_platform	16.1	cpe:2.3:a:redhat:openstack_platform:16.1:::::::*
redhat	openstack_platform	16.2	cpe:2.3:a:redhat:openstack_platform:16.2:::::::*

References for CVE-2021-20267

URL	Tags
https://bugzilla.redhat.com/show_bug.cgi?id=1934330	Issue Tracking Patch Third Party Advisory
https://security.openstack.org/ossa/OSSA-2021-001.html	Patch Vendor Advisory

URL

CVE-2021-20267

Exploit prediction scoring system (EPSS) score for CVE-2021-20267

Common vulnerability scoring system (CVSS) metrics for CVE-2021-20267

Weakness enumeration for CVE-2021-20267

GitHub Security Advisory for CVE-2021-20267

OS Trackers for CVE-2021-20267

Affected software / configurations for CVE-2021-20267

References for CVE-2021-20267