How severe is CVE-2021-20267?

CVE-2021-20267 has a CVSS score of 7.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-20267?

CVE-2021-20267 affects the following packages: neutron (PyPI), neutron (PyPI), neutron (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2021-20267?

Update neutron to 16.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-20267 is resolved across your whole dependency graph.

How do I detect CVE-2021-20267 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for neutron, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-20267 if there is no patch (or I can't update yet)?

Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Is CVE-2021-20267 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-20267 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

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

CVE-2021-20267 has an EPSS (Exploit Prediction Scoring System) score of 1.0%, placing it in the 64th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-20267?

CVE-2021-20267 is classified as CWE-345 (CWE-345). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-20267 published, and has it been updated?

CVE-2021-20267 was published on May 28, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2021-20267 — neutron

HIGH

CVE-2021-20267 is a high-severity (CVSS 7.1) CWE-345 vulnerability in neutron. A fix is available for neutron — see the affected versions and patch details below.

Openstack Neutron has Insufficient Verification of IPv6 addresses

Also known asGHSA-w8hx-f868-pvchPYSEC-2021-136

Published

May 28, 2021

Updated

Oct 24, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.0%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs64th percentile — riskier than 64% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

3 pkgs affected

🐍neutron🐍neutron🐍neutron

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`neutron`	≥ 16.0.0&&< 16.3.1	16.3.1`pip install --upgrade 'neutron==16.3.1'`
🐍PyPI	`neutron`	all versions	15.3.3`pip install --upgrade 'neutron==15.3.3'`
🐍PyPI	`neutron`	≥ 17.0.0&&< 17.1.1	17.1.1`pip install --upgrade 'neutron==17.1.1'`

Affected Products

2 products · 7 configurations

Application

neutronopenstack

≥ 17.0.0 && < 17.1.3

1 version

18.0.0

Application

openstack platformredhat

4 versions

10.013.016.116.2

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for neutron, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update neutron to 16.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-20267 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

Workaround published by Red Hat

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.

Source: Red Hat security advisory for CVE-2021-20267 (CC BY 4.0)

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-20267 in your dependencies?

Find it across PyPI, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

7.1/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

Low

Integrity

None

Availability

High

Raw vector

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

CWE Classification

CWE-345CWE-345

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

OpenSSF Scorecard

Package health score

neutron

3.2/10

Code-Review0/10

Maintained10/10

Branch-Protection0/10

Assessed Oct 19, 2026

Timeline

Disclosed

May 28, 2021

Last updated

Oct 24, 2026

Identifiers

CVE-2021-20267

GHSA-w8hx-f868-pvch

PYSEC-2021-136

References

Advisorynvd.nist.gov · CVE 2021 20267 Fixbugzilla.redhat.com · show bug.cgi Fixsecurity.openstack.org · OSSA 2021 001 Webgithub.com · PYSEC 2021 136.yaml Packagegithub.com · neutron

Related vulnerabilities

This CVE is high severity; 3 of 8 other CVEs affecting neutron are rated as high or higher (top: high).

CVE-2026-50266CVE-2026-49299CVE-2024-53916CVE-2023-3637CVE-2022-3277CVE-2021-40797CVE-2021-40085CVE-2021-38598

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 24, 2026