10 KiB
Docker --privileged
{% hint style="success" %}
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What Affects
When you run a container as privileged these are the protections you are disabling:
Mount /dev
In a privileged container, all the devices can be accessed in /dev/. Therefore you can escape by mounting the disk of the host.
{% tabs %} {% tab title="Inside default container" %}
# docker run --rm -it alpine sh
ls /dev
console fd mqueue ptmx random stderr stdout urandom
core full null pts shm stdin tty zero
{% endtab %}
{% tab title="Inside Privileged Container" %}
# docker run --rm --privileged -it alpine sh
ls /dev
cachefiles mapper port shm tty24 tty44 tty7
console mem psaux stderr tty25 tty45 tty8
core mqueue ptmx stdin tty26 tty46 tty9
cpu nbd0 pts stdout tty27 tty47 ttyS0
[...]
{% endtab %} {% endtabs %}
Read-only kernel file systems
Kernel file systems provide a mechanism for a process to modify the behavior of the kernel. However, when it comes to container processes, we want to prevent them from making any changes to the kernel. Therefore, we mount kernel file systems as read-only within the container, ensuring that the container processes cannot modify the kernel.
{% tabs %} {% tab title="Inside default container" %}
# docker run --rm -it alpine sh
mount | grep '(ro'
sysfs on /sys type sysfs (ro,nosuid,nodev,noexec,relatime)
cpuset on /sys/fs/cgroup/cpuset type cgroup (ro,nosuid,nodev,noexec,relatime,cpuset)
cpu on /sys/fs/cgroup/cpu type cgroup (ro,nosuid,nodev,noexec,relatime,cpu)
cpuacct on /sys/fs/cgroup/cpuacct type cgroup (ro,nosuid,nodev,noexec,relatime,cpuacct)
{% endtab %}
{% tab title="Inside Privileged Container" %}
# docker run --rm --privileged -it alpine sh
mount | grep '(ro'
{% endtab %} {% endtabs %}
Masking over kernel file systems
The /proc file system is selectively writable but for security, certain parts are shielded from write and read access by overlaying them with tmpfs, ensuring container processes can't access sensitive areas.
{% hint style="info" %} tmpfs is a file system that stores all the files in virtual memory. tmpfs doesn't create any files on your hard drive. So if you unmount a tmpfs file system, all the files residing in it are lost for ever. {% endhint %}
{% tabs %} {% tab title="Inside default container" %}
# docker run --rm -it alpine sh
mount | grep /proc.*tmpfs
tmpfs on /proc/acpi type tmpfs (ro,relatime)
tmpfs on /proc/kcore type tmpfs (rw,nosuid,size=65536k,mode=755)
tmpfs on /proc/keys type tmpfs (rw,nosuid,size=65536k,mode=755)
{% endtab %}
{% tab title="Inside Privileged Container" %}
# docker run --rm --privileged -it alpine sh
mount | grep /proc.*tmpfs
{% endtab %} {% endtabs %}
Linux capabilities
Container engines launch the containers with a limited number of capabilities to control what goes on inside of the container by default. Privileged ones have all the capabilities accesible. To learn about capabilities read:
{% content-ref url="../linux-capabilities.md" %} linux-capabilities.md {% endcontent-ref %}
{% tabs %} {% tab title="Inside default container" %}
# docker run --rm -it alpine sh
apk add -U libcap; capsh --print
[...]
Current: cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap=eip
Bounding set =cap_chown,cap_dac_override,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_net_bind_service,cap_net_raw,cap_sys_chroot,cap_mknod,cap_audit_write,cap_setfcap
[...]
{% endtab %}
{% tab title="Inside Privileged Container" %}
# docker run --rm --privileged -it alpine sh
apk add -U libcap; capsh --print
[...]
Current: =eip cap_perfmon,cap_bpf,cap_checkpoint_restore-eip
Bounding set =cap_chown,cap_dac_override,cap_dac_read_search,cap_fowner,cap_fsetid,cap_kill,cap_setgid,cap_setuid,cap_setpcap,cap_linux_immutable,cap_net_bind_service,cap_net_broadcast,cap_net_admin,cap_net_raw,cap_ipc_lock,cap_ipc_owner,cap_sys_module,cap_sys_rawio,cap_sys_chroot,cap_sys_ptrace,cap_sys_pacct,cap_sys_admin,cap_sys_boot,cap_sys_nice,cap_sys_resource,cap_sys_time,cap_sys_tty_config,cap_mknod,cap_lease,cap_audit_write,cap_audit_control,cap_setfcap,cap_mac_override,cap_mac_admin,cap_syslog,cap_wake_alarm,cap_block_suspend,cap_audit_read
[...]
{% endtab %} {% endtabs %}
You can manipulate the capabilities available to a container without running in --privileged mode by using the --cap-add and --cap-drop flags.
Seccomp
Seccomp is useful to limit the syscalls a container can call. A default seccomp profile is enabled by default when running docker containers, but in privileged mode it is disabled. Learn more about Seccomp here:
{% content-ref url="seccomp.md" %} seccomp.md {% endcontent-ref %}
{% tabs %} {% tab title="Inside default container" %}
# docker run --rm -it alpine sh
grep Seccomp /proc/1/status
Seccomp: 2
Seccomp_filters: 1
{% endtab %}
{% tab title="Inside Privileged Container" %}
# docker run --rm --privileged -it alpine sh
grep Seccomp /proc/1/status
Seccomp: 0
Seccomp_filters: 0
{% endtab %} {% endtabs %}
# You can manually disable seccomp in docker with
--security-opt seccomp=unconfined
Also, note that when Docker (or other CRIs) are used in a Kubernetes cluster, the seccomp filter is disabled by default
AppArmor
AppArmor is a kernel enhancement to confine containers to a limited set of resources with per-program profiles. When you run with the --privileged flag, this protection is disabled.
{% content-ref url="apparmor.md" %} apparmor.md {% endcontent-ref %}
# You can manually disable seccomp in docker with
--security-opt apparmor=unconfined
SELinux
Running a container with the --privileged flag disables SELinux labels, causing it to inherit the label of the container engine, typically unconfined, granting full access similar to the container engine. In rootless mode, it uses container_runtime_t, while in root mode, spc_t is applied.
{% content-ref url="../selinux.md" %} selinux.md {% endcontent-ref %}
# You can manually disable selinux in docker with
--security-opt label:disable
What Doesn't Affect
Namespaces
Namespaces are NOT affected by the --privileged flag. Even though they don't have the security constraints enabled, they do not see all of the processes on the system or the host network, for example. Users can disable individual namespaces by using the --pid=host, --net=host, --ipc=host, --uts=host container engines flags.
{% tabs %} {% tab title="Inside default privileged container" %}
# docker run --rm --privileged -it alpine sh
ps -ef
PID USER TIME COMMAND
1 root 0:00 sh
18 root 0:00 ps -ef
{% endtab %}
{% tab title="Inside --pid=host Container" %}
# docker run --rm --privileged --pid=host -it alpine sh
ps -ef
PID USER TIME COMMAND
1 root 0:03 /sbin/init
2 root 0:00 [kthreadd]
3 root 0:00 [rcu_gp]ount | grep /proc.*tmpfs
[...]
{% endtab %} {% endtabs %}
User namespace
By default, container engines don't utilize user namespaces, except for rootless containers, which require them for file system mounting and using multiple UIDs. User namespaces, integral for rootless containers, cannot be disabled and significantly enhance security by restricting privileges.
References
{% hint style="success" %}
Learn & practice AWS Hacking:HackTricks Training AWS Red Team Expert (ARTE)
Learn & practice GCP Hacking: HackTricks Training GCP Red Team Expert (GRTE)
Support HackTricks
- Check the subscription plans!
- Join the 💬 Discord group or the telegram group or follow us on Twitter 🐦 @hacktricks_live.
- Share hacking tricks by submitting PRs to the HackTricks and HackTricks Cloud github repos.