Canonical LXD Source Container Identification Vulnerability via cmdline Spoofing in devLXD Server

Impact

In LXD's devLXD server, the source container identification process uses process cmdline (command line) information, allowing attackers to impersonate other containers by spoofing process names.

The core issue lies in the findContainerForPID function in lxd/api_devlxd.go.
This function identifies senders through two steps as shown below:

1. cmdline-based identification: Check while tracing back through parent processes, and if it starts with [lxc monitor], extract the project name and container name from that process name in the format projectName_containerName.
2. PID namespace-based identification: If not found in Step 1, check against all containers' PID namespaces.

https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/api_devlxd.go#L166-L276

Attackers can exploit Step 1 processing to impersonate arbitrary containers across projects by spoofing process names.

Reproduction Steps

1. Access devLXD server from a normal container (e.g., EEEE):

root@EEEE:~# curl --unix-socket /dev/lxd/sock http://lxd-host/1.0/meta-data
instance-id: 9f928574-2561-4eff-af82-a68e57d3c68b
local-hostname: EEEE

2. Use exec -a to spoof process name and impersonate another container (DDDD):

root@EEEE:~# bash -c "exec -a '[lxc monitor]' curl --unix-socket /dev/lxd/sock http://lxd-host/1.0/meta-data -x 'test-project_DDDD'"
instance-id: 1bb2f1c3-3ad2-4cd6-9965-67b14c3582cc
local-hostname: DDDD

This attack successfully obtains metadata (instance-id, local-hostname) of another container
DDDD from within container EEEE.

Risk

This vulnerability allows attackers to perform the following actions:

1. Theft of other containers' metadata information
   Obtaining other containers' information via devLXD API's /1.0/meta-data endpoint:
   https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/devlxd.go#L295-L304

2. Obtaining other containers' configuration information via devLXD API's /1.0/config and /1.0/config/{key} endpoints:
   https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/devlxd.go#L175-L221
   https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/devlxd.go#L228-L267

3. Obtaining other containers' device information via devLXD API's /1.0/devices endpoint:
   https://github.com/canonical/lxd/blob/43d5189564d27f6161b430ed258c8b56603c2759/lxd/devlxd.go#L377-L395
   Particularly in environments where multiple projects run containers on the same LXD host,
   inter-project information leakage may occur. The attack prerequisite is root privileges within
   any container.

Countermeasures

While containers basically run in separate PID namespaces, based on investigation, the [lxc monitor] process runs in the same PID namespace as the LXD execution process. Therefore, the problem can be resolved by modifying the implementation to use cmdline information only when the PID namespace of the target process matches the PID namespace of the process running LXD.

Patches

References

Reported by GMO Flatt Security Inc.