Ecosyste.ms: Advisories

Security Advisories: GSA_kwCzR0hTQS1wOXY4LXE1bTQtcGY0Ns4ABDb3

CVE-2024-5138: snapd snapctl auth bypass

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:

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

Permalink: https://github.com/advisories/GHSA-p9v8-q5m4-pf46
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS1wOXY4LXE1bTQtcGY0Ns4ABDb3
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: 13 days ago
Updated: 13 days ago

CVSS Score: 4.0
CVSS vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

EPSS Percentage: 0.00045
EPSS Percentile: 0.17541

Identifiers: GHSA-p9v8-q5m4-pf46, CVE-2024-5138
References:

• https://github.com/canonical/snapd/security/advisories/GHSA-p9v8-q5m4-pf46
• https://github.com/canonical/snapd/commit/68ee9c6aa916ab87dbfd9a26030690f2cabf1e14
• https://bugs.launchpad.net/snapd/+bug/2065077
• https://ubuntu.com/security/CVE-2024-5138
• https://www.cve.org/CVERecord?id=CVE-2024-5138
• https://github.com/advisories/GHSA-p9v8-q5m4-pf46

Repository: https://github.com/canonical/snapd
Blast Radius: 6.7

Affected Packages