CVE-2023-30549

Apptainer is an open source container platform for Linux. There is an ext4
use-after-free flaw that is exploitable through versions of Apptainer <
1.1.0 and installations that include apptainer-suid < 1.1.8 on older
operating systems where that CVE has not been patched. That includes Red
Hat Enterprise Linux 7, Debian 10 buster (unless the linux-5.10 package is
installed), Ubuntu 18.04 bionic and Ubuntu 20.04 focal. Use-after-free
flaws in the kernel can be used to attack the kernel for denial of service
and potentially for privilege escalation. Apptainer 1.1.8 includes a patch
that by default disables mounting of extfs filesystem types in setuid-root
mode, while continuing to allow mounting of extfs filesystems in non-setuid
“rootless” mode using fuse2fs. Some workarounds are possible. Either do not
install apptainer-suid (for versions 1.1.0 through 1.1.7) or set allow setuid = no in apptainer.conf. This requires having unprivileged user
namespaces enabled and except for apptainer 1.1.x versions will disallow
mounting of sif files, extfs files, and squashfs files in addition to
other, less significant impacts. (Encrypted sif files are also not
supported unprivileged in apptainer 1.1.x.). Alternatively, use the limit containers options in apptainer.conf/singularity.conf to limit sif files
to trusted users, groups, and/or paths, and set allow container extfs = no to disallow mounting of extfs overlay files. The latter option by
itself does not disallow mounting of extfs overlay partitions inside SIF
files, so that’s why the former options are also needed.

Bugs

• <http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1035026&gt;