CVE-2021-40085 is a medium-severity (CVSS 6.5) vulnerability in neutron. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for neutron — see the affected versions and patch details below.
OpenStack Neutron vulnerable to authenticated attackers reconfiguring dnsmasq via crafted extra_dhcp_opts value
EPSS Exploitation Probability
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
neutron🐍neutron🐍neutronReal-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
An issue was discovered in OpenStack Neutron before 16.4.1, 17.x before 17.2.1, and 18.x before 18.1.1. Authenticated attackers can reconfigure dnsmasq via a crafted extra_dhcp_opts value.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | neutron | all versions | 16.4.1pip install --upgrade 'neutron==16.4.1' |
| 🐍PyPI | neutron | ≥ 17.0.0&&< 17.2.1 | 17.2.1pip install --upgrade 'neutron==17.2.1' |
| 🐍PyPI | neutron | ≥ 18.0.0&&< 18.1.1 | 18.1.1pip install --upgrade 'neutron==18.1.1' |
Affected Products
debian linuxdebianneutronopenstackResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
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 16.4.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-40085 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
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.
IMPORTANT impact affects Red Hat OpenStack Platform deployments using openstack-neutron. An authenticated attacker can submit crafted extra_dhcp_opts values to alter the dnsmasq configuration, crash the service, or change parameters for other tenants sharing the same interface. The input may also trigger a…
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-2021-40085 (CC BY 4.0)
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenStack Platform 10.0 (Newton) | openstack-neutron-1:9.4.1-56.el7ost | RHSA-2021:3502 |
| Red Hat OpenStack Platform 13.0 - ELS | openstack-neutron-1:12.1.1-42.1.el7ost | RHSA-2021:3503 |
| Red Hat OpenStack Platform 16.1 | openstack-neutron-1:15.2.1-1.20210409073447.el8ost | RHSA-2021:3481 |
| Red Hat OpenStack Platform 16.2 | openstack-neutron-1:15.3.5-2.20210608154813.el8ost.3 | RHSA-2021:3488 |
Frequently Asked Questions
Is CVE-2021-40085 in your dependencies?
Find it across PyPI, including transitive dependencies.