Consider the following aspects to ensure that your Incus installation is secure:
Keep your operating system up-to-date and install all available security patches.
Use only supported Incus versions.
Restrict access to the Incus daemon and the remote API.
Do not use privileged containers unless required. If you use privileged containers, put appropriate security measures in place. See the LXC security page for more information.
Configure your network interfaces to be secure.
See the following sections for detailed information.
If you discover a security issue, see the Incus security policy for information on how to report the issue.
Never use unsupported Incus versions in a production environment.
Incus has two types of releases:
For feature releases, only the latest one is supported, and we usually don’t do point releases. Instead, users are expected to wait until the next release.
For LTS releases, we do periodic bugfix releases that include an accumulation of bugfixes from the feature releases. Such bugfix releases do not include new features.
Access to the Incus daemon#
Incus is a daemon that can be accessed locally over a Unix socket or, if configured, remotely over a TLS socket. Anyone with access to the socket can fully control Incus, which includes the ability to attach host devices and file systems or to tweak the security features for all instances.
Therefore, make sure to restrict the access to the daemon to trusted users.
Local access to the Incus daemon#
The Incus daemon runs as root and provides a Unix socket for local communication.
Access control for Incus is based on group membership.
The root user and all members of the
incus-admin group can interact with the local daemon.
Local access to Incus through the Unix socket always grants full access to Incus. This includes the ability to attach file system paths or devices to any instance as well as tweak the security features on any instance.
Therefore, you should only give such access to users who you’d trust with root access to your system.
Access to the remote API#
By default, access to the daemon is only possible locally.
By setting the
core.https_address configuration option, you can expose the same API over the network on a TLS socket.
See How to expose Incus to the network for instructions.
Remote clients can then connect to Incus and access any image that is marked for public use.
There are several ways to authenticate remote clients as trusted clients to allow them to access the API. See Remote API authentication for details.
In a production setup, you should set
core.https_address to the single address where the server should be available (rather than any address on the host).
In addition, you should set firewall rules to allow access to the Incus port only from authorized hosts/subnets.
Incus containers can use a wide range of features for security.
By default, containers are unprivileged, meaning that they operate inside a user namespace, restricting the abilities of users in the container to that of regular users on the host with limited privileges on the devices that the container owns.
If data sharing between containers isn’t needed, you can enable
security.idmap.isolated, which will use non-overlapping UID/GID maps for each container, preventing potential DoS attacks on other containers.
Incus can also run privileged containers. Note, however, that those aren’t root safe, and a user with root access in such a container will be able to DoS the host as well as find ways to escape confinement.
More details on container security and the kernel features we use can be found on the LXC security page.
Container name leakage#
The default server configuration makes it easy to list all cgroups on a system and, by extension, all running containers.
You can prevent this name leakage by blocking access to
/proc/sched_debug before you start any containers.
To do so, run the following commands:
chmod 400 /proc/sched_debug chmod 700 /sys/kernel/slab/
Make sure to configure your network interfaces to be secure. Which aspects you should consider depends on the networking mode you decide to use.
Bridged NIC security#
The default networking mode in Incus is to provide a “managed” private network bridge that each instance connects to.
In this mode, there is an interface on the host called
incusbr0 that acts as the bridge for the instances.
The host runs an instance of
dnsmasq for each managed bridge, which is responsible for allocating IP addresses and providing both authoritative and recursive DNS services.
Instances using DHCPv4 will be allocated an IPv4 address, and a DNS record will be created for their instance name. This prevents instances from being able to spoof DNS records by providing false host name information in the DHCP request.
dnsmasq service also provides IPv6 router advertisement capabilities.
This means that instances will auto-configure their own IPv6 address using SLAAC, so no allocation is made by
However, instances that are also using DHCPv4 will also get an AAAA DNS record created for the equivalent SLAAC IPv6 address.
This assumes that the instances are not using any IPv6 privacy extensions when generating IPv6 addresses.
In this default configuration, whilst DNS names cannot not be spoofed, the instance is connected to an Ethernet bridge and can transmit any layer 2 traffic that it wishes, which means an instance that is not trusted can effectively do MAC or IP spoofing on the bridge.
In the default configuration, it is also possible for instances connected to the bridge to modify the Incus host’s IPv6 routing table by sending (potentially malicious) IPv6 router advertisements to the bridge.
This is because the
incusbr0 interface is created with
/proc/sys/net/ipv6/conf/incusbr0/accept_ra set to
2, meaning that the Incus host will accept router advertisements even though
forwarding is enabled (see
/proc/sys/net/ipv4/* Variables for more information).
However, Incus offers several bridged NIC security features that can be used to control the type of traffic that an instance is allowed to send onto the network. These NIC settings should be added to the profile that the instance is using, or they can be added to individual instances, as shown below.
The following security features are available for bridged NICs:
Prevent the instance from spoofing another instance’s MAC address
Prevent the instance from spoofing another instance’s IPv4 address (enables
Prevent the instance from spoofing another instance’s IPv6 address (enables
One can override the default bridged NIC settings from the profile on a per-instance basis using:
incus config device override <instance> <NIC> security.mac_filtering=true
Used together, these features can prevent an instance connected to a bridge from spoofing MAC and IP addresses.
These options are implemented using either
nftables, depending on what is available on the host.
It’s worth noting that those options effectively prevent nested containers from using the parent network with a different MAC address (i.e using bridged or
The IP filtering features block ARP and NDP advertisements that contain a spoofed IP, as well as blocking any packets that contain a spoofed source address.
security.ipv6_filtering is enabled and the instance cannot be allocated an IP address (because
ipvX.address=none or there is no DHCP service enabled on the bridge), then all IP traffic for that protocol is blocked from the instance.
security.ipv6_filtering is enabled, IPv6 router advertisements are blocked from the instance.
security.ipv6_filtering is enabled, any Ethernet frames that are not ARP, IPv4 or IPv6 are dropped.
This prevents stacked VLAN Q-in-Q (802.1ad) frames from bypassing the IP filtering.
Routed NIC security#
An alternative networking mode is available called “routed”.
It provides a virtual Ethernet device pair between container and host.
In this networking mode, the Incus host functions as a router, and static routes are added to the host directing traffic for the container’s IPs towards the container’s
By default, the
veth interface created on the host has its
accept_ra setting disabled to prevent router advertisements from the container modifying the IPv6 routing table on the Incus host.
In addition to that, the
rp_filter on the host is set to
1 to prevent source address spoofing for IPs that the host does not know the container has.