An access control bypass and information disclosure vulnerability exists in the base AppArmor security profile configuration of Canonical snapd. The abstraction rules located in /etc/apparmor.d/abstractions/nss-systemd (inherited via ) inadvertently permit strictly confined snap applications, which lack the privileged account-control interface, to interact directly with the io.systemd.Multiplexer and io.systemd.NameServiceSwitch UNIX domain sockets under /run/systemd/userdb/. On systems where the systemd-userdbd service is installed and operational, the service fails to distinguish between an unconfined root user on the host system and a restricted root user running within a snap application's sandbox (such as a daemon or configuration hook). Because systemd-userdbd returns "complete" user records—including sensitive hashed user passwords from /etc/shadow—when queried by a process running as root, a compromised or malicious strictly confined snap executing code as root can successfully query the Varlink interface to retrieve all system password hashes, bypassing intended snap sandbox restrictions. This issue is mitigated by the fact that systemd-userdbd is not installed by default on standard Ubuntu deployments.

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.

Last updated 25 August 2025