Impact
A snap with prior permissions to create a mount entry on the host, such as firefox, normally uses the permission from one of the per-snap hook programs. A unprivileged users cannot normally trigger that behaviour by using snap run --shell firefox followed by snapctl mount, since snapd validates the requesting user identity (root or non-root). The issue allows unprivileged users to bypass that check by crafting a malicious command line vector which confuses snapd into thinking the help message is requested.
Unprivileged user on a default installation of Ubuntu, where firefox is as provided as a snap, may cause a denial-of-service attack by repeatedly mounting hunspell database over and over and eventually exhausting system memory.
Other attacks, reliant on the same underying mechanism (mount), are possible. In all cases the snap must be installed and grated permission to perform this action (by connecting an appropriate snap interface), which requires administrative privileges. As such we are focusing on the case of default installation where an unprivileged user may exploit this behavior.
Patches
Patch: canonical/snapd@68ee9c6
Release: Available from Snapd 2.64
Workarounds
Users may disconnect any instances of the mount-control interface to prevent snapd from creating such mount points. For example, the firefox snap has the host-hunspell plug, which is of type mount-control. The interface can be disconnected with:
sudo snap disconnect firefox:host-hunspell
References
The original bug report was made on Launchpad: https://bugs.launchpad.net/snapd/+bug/2065077
CVE.org: https://www.cve.org/CVERecord?id=CVE-2024-5138
Canonical: https://ubuntu.com/security/CVE-2024-5138
References
rmcnamara-snyk Reporter
Impact
A snap with prior permissions to create a mount entry on the host, such as firefox, normally uses the permission from one of the per-snap hook programs. A unprivileged users cannot normally trigger that behaviour by using
snap run --shell firefoxfollowed bysnapctl mount, since snapd validates the requesting user identity (root or non-root). The issue allows unprivileged users to bypass that check by crafting a malicious command line vector which confuses snapd into thinking the help message is requested.Unprivileged user on a default installation of Ubuntu, where firefox is as provided as a snap, may cause a denial-of-service attack by repeatedly mounting hunspell database over and over and eventually exhausting system memory.
Other attacks, reliant on the same underying mechanism (mount), are possible. In all cases the snap must be installed and grated permission to perform this action (by connecting an appropriate snap interface), which requires administrative privileges. As such we are focusing on the case of default installation where an unprivileged user may exploit this behavior.
Patches
Patch: canonical/snapd@68ee9c6
Release: Available from Snapd 2.64
Workarounds
Users may disconnect any instances of the mount-control interface to prevent snapd from creating such mount points. For example, the firefox snap has the
host-hunspellplug, which is of typemount-control. The interface can be disconnected with:References
The original bug report was made on Launchpad: https://bugs.launchpad.net/snapd/+bug/2065077
CVE.org: https://www.cve.org/CVERecord?id=CVE-2024-5138
Canonical: https://ubuntu.com/security/CVE-2024-5138
References