CVE-2021-40085: OpenStack Neutron dnsmasq Reconfiguration Vulnerability
Summary
CVE-2021-40085: An issue was discovered in OpenStack Neutron before 16.4.1, 17.x before 17.2.1, and 18.x before 18.1.1. Affects neutron across 3 version ranges.
< 16.4.1
>= 17.0.0, < 17.2.1
>= 18.0.0, < 18.1.1
Fixed in 16.4.1, 17.2.1 or 18.1.1, depending on the release line you run. How to fix ↓
Also tracked for
- neutron · Debian:11
The same CVE-2021-40085 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
OpenStack Neutron is a networking service that provides connectivity between virtual machines (VMs) and other network resources in an OpenStack environment. It manages the networking infrastructure and provides services such as IP address allocation, routing, and security groups. Neutron uses dnsmasq, a lightweight DNS and DHCP server, to provide DHCP services for VMs. This vulnerability allows authenticated attackers to reconfigure dnsmasq by exploiting a crafted extra_dhcp_opts value.
Vulnerability Detail
The vulnerability in OpenStack Neutron allows authenticated attackers to manipulate the configuration of dnsmasq, which can have severe consequences. By providing a specially crafted extra_dhcp_opts value, attackers can modify the behavior of dnsmasq, potentially leading to unauthorized access, network disruptions, or other malicious activities. This vulnerability affects versions of Neutron before 16.4.1, 17.x before 17.2.1, and 18.x before 18.1.1.
How To Fix
Latest published version: 29.0.0 as of 22 Oct 2026
pip install --upgrade "neutron==29.0.0"Upgrading to it may include breaking changes; the versions below are the minimum fixed release for this vulnerability.
If you can't move to the latest
The minimum fixed version depends on the release line you run.
-
< 16.4.116.4.1pip install --upgrade "neutron==16.4.1" -
>= 17.0.0, < 17.2.117.2.1pip install --upgrade "neutron==17.2.1" -
>= 18.0.0, < 18.1.118.1.1pip install --upgrade "neutron==18.1.1"
Tip — Not sure which release line you're on? Vulert can find the fix for the version you are using. Scan free →
Workaround
There is no known workaround for this vulnerability. It is highly recommended to apply the official patches or upgrade to the fixed versions mentioned above.
Conclusion
The OpenStack Neutron dnsmasq reconfiguration vulnerability (CVE-2021-40085) allows authenticated attackers to manipulate the behavior of dnsmasq, potentially leading to unauthorized access or network disruptions. It is crucial to apply the recommended patches or upgrade to the fixed versions to mitigate this vulnerability. For further support on vulnerability remediation, contact DevNack.com.
See every vulnerability recorded for neutron →
FAQ
OpenStack Neutron is a networking service in the OpenStack cloud platform that provides connectivity between virtual machines and other network resources.
Dnsmasq is a lightweight DNS and DHCP server used by OpenStack Neutron to provide DHCP services for virtual machines.
This vulnerability allows authenticated attackers to reconfigure dnsmasq, potentially leading to unauthorized access, network disruptions, or other malicious activities.
Versions of OpenStack Neutron before 16.4.1, 17.x before 17.2.1, and 18.x before 18.1.1 are affected by this vulnerability.
To fix this vulnerability, it is recommended to upgrade to the latest patched version of OpenStack Neutron (16.4.1, 17.2.1, or 18.1.1).
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