CVE-2020-15229

Description

Singularity (an open source container platform) from version 3.1.1 through 3.6.3 has a vulnerability. Due to insecure handling of path traversal and the lack of path sanitization within `unsquashfs`, it is possible to overwrite/create any files on the host filesystem during the extraction with a crafted squashfs filesystem. The extraction occurs automatically for unprivileged (either installation or with `allow setuid = no`) run of Singularity when a user attempt to run an image which is a local SIF image or a single file containing a squashfs filesystem and is coming from remote sources `library://` or `shub://`. Image build is also impacted in a more serious way as it can be used by a root user, allowing an attacker to overwrite/create files leading to a system compromise, so far bootstrap methods `library`, `shub` and `localimage` are triggering the squashfs extraction. This issue is addressed in Singularity 3.6.4. All users are advised to upgrade to 3.6.4 especially if they use Singularity mainly for building image as root user. There is no solid workaround except to temporary avoid to use unprivileged mode with single file images in favor of sandbox images instead. Regarding image build, temporary avoid to build from `library` and `shub` sources and as much as possible use `--fakeroot` or a VM for that.

Gravité et risque d'exploitation

CVE-2020-15229 obtient un score CVSS de 8.2/10, soit une gravité élevée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 2.05 %, ce qui la place devant 80.9 % des CVE référencées.

Que faire ?

• Vérifiez si singularity (versions < 3.6.4) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://github.com/hpcng/singularity/security/advisories/GHSA-7gcp-w6ww-2xv9
• https://github.com/hpcng/singularity/blob/v3.6.4/CHANGELOG.md#security-related-fixes
• https://github.com/hpcng/singularity/pull/5611
• https://github.com/hpcng/singularity/commit/eba3dea260b117198fdb6faf41f2482ab2f8d53e
• http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00071.html
• http://lists.opensuse.org/opensuse-security-announce/2020-10/msg00070.html
• http://lists.opensuse.org/opensuse-security-announce/2020-11/msg00009.html