Hi everyone,

Qualys discovered another Local Privilege Escalation (LPE) in snapd snap-confine, via Capabilities misconfiguration. Qualys will send an email on top of this one with their report, but in the meantime, for this vulnerability we assigned CVE-2026-8933, with CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H 7.8 HIGH

The upstream version of snapd containing the fix will be 2.76.1.

Also in this version we are fixing/disclosing other two vulnerabilities - CVE-2024-5300 AppArmor Base Profile Misconfiguration in snapd Permits Confined Snaps Unauthorized Access to Hashed Passwords via systemd-userdbd CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N 5.6 MEDIUM Credits: James Henstridge

- CVE-2026-15226 snapd snap-confine Sandbox Confinement Bypass via Omission of setuid Restriction in Seccomp Templates CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:N 8.4 HIGH Credits: Zygmunt Krynicki

In Ubuntu those fixes will land in:

Xenial (16.04): snapd - 2.61.4ubuntu0.16.04.1+esm4 Bionic (18.04): snapd - 2.61.4ubuntu0.18.04.1+esm4 Focal (20.04): snapd - 2.67.1+20.04ubuntu1~esm3 Jammy (22.04): snapd - 2.76+ubuntu22.04.1 Noble (24.04): snapd - 2.76+ubuntu24.04.1 Resolute (26.04): snapd - 2.76+ubuntu26.04.3

And we will soon be publishing an advisory: https://ubuntu.com/security/notices/USN-8579-1

We want to thanks again Qualys, Zygmunt and James for their work and patience!

Thanks, Eduardo

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.

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: https://github.com/canonical/snapd/commit/68ee9c6aa916ab87dbfd9a26030690f2cabf1e14 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:

sh 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

Last updated 24 July 2024

Last updated 25 August 2025

Last updated 25 August 2025

Last updated 25 August 2025

A race condition existed in the snapd 2.54.2 snap-confine binary when preparing a private mount namespace for a snap. This could allow a local attacker to gain root privileges by bind-mounting their own contents inside the snap's private mount namespace and causing snap-confine to execute arbitrary code and hence gain privilege escalation. Fixed in snapd versions 2.54.3+18.04, 2.54.3+20.04 and 2.54.3+21.10.1

cloud-init as managed by snapd on Ubuntu Core 16 and Ubuntu Core 18 devices was run without restrictions on every boot, which a physical attacker could exploit by crafting cloud-init user-data/meta-data via external media to perform arbitrary changes on the device to bypass intended security mechanisms such as full disk encryption. This issue did not affect traditional Ubuntu systems. Fixed in snapd version 2.45.2, revision 8539 and core version 2.45.2, revision 9659.

A vulnerability in the seccomp filters of Canonical snapd before version 2.37.4 allows a strict mode snap to insert characters into a terminal on a 64-bit host. The seccomp rules were generated to match 64-bit ioctl(2) commands on a 64-bit platform; however, the Linux kernel only uses the lower 32 bits to determine which ioctl(2) commands to run. This issue affects: Canonical snapd versions prior to 2.37.4.

Canonical snapd before version 2.37.1 incorrectly performed socket owner validation, allowing an attacker to run arbitrary commands as root. This issue affects: Canonical snapd versions prior to 2.37.1.