In snapd versions prior to 2.62, snapd failed to properly check the destination of symbolic links when extracting a snap. The snap format is a squashfs file-system image and so can contain symbolic links and other file types. Various file entries within the snap squashfs image (such as icons and desktop files etc) are directly read by snapd when it is extracted. An attacker who could convince a user to install a malicious snap which contained symbolic links at these paths could then cause snapd to write out the contents of the symbolic link destination into a world-readable directory. This in-turn could allow an unprivileged user to gain access to privileged information.

In snapd versions prior to 2.62, snapd failed to properly check the file type when extracting a snap. The snap format is a squashfs file-system image and so can contain files that are non-regular files (such as pipes or sockets etc). Various file entries within the snap squashfs image (such as icons etc) are directly read by snapd when it is extracted. An attacker who could convince a user to install a malicious snap which contained non-regular files at these paths could then cause snapd to block indefinitely trying to read from such files and cause a denial of service.

In snapd versions prior to 2.62, when using AppArmor for enforcement of sandbox permissions, snapd failed to restrict writes to the $HOME/bin path. In Ubuntu, when this path exists, it is automatically added to the users PATH. An attacker who could convince a user to install a malicious snap which used the 'home' plug could use this vulnerability to install arbitrary scripts into the users PATH which may then be run by the user outside of the expected snap sandbox and hence allow them to escape confinement.

Race condition in snap-confine's must_mkdir_and_open_with_perms()