Apptainer has incorrect path matching for 'limit container paths' directive

Impact

The limit container paths directive in apptainer.conf is intended to allow a system administrator limit the paths from which containers can be run, under setuid mode. Due to incorrect matching of a path string, sibling directories with similar names may incorrectly be allowed.

For example, the configuration:

 1limit container paths = /data/safe

Will also allow containers in /data/safe-but-unsafe to be run.

Patches

The issue is patched in apptainer version 1.5.1.

Workarounds

If developers do not use setuid mode or do not use the limit container paths functionality, then this issue does not affect their installation. Note that, as documented [1], if user namespaces are allowed for unrestricted use then this functionality does not stop users from running any container of their choice.

If developers do use the limit container paths functionality they are advised to update.

Credit

This vulnerability was discovered and disclosed to the Apptainer project by Dave Trudgian of Sylabs.

Resources

[1] https://apptainer.org/docs/admin/latest/configfiles.html#limiting-container-execution