CVE-2020-15229 in Sylabs and OpenSuse Products
Published on October 14, 2020

Path traversal and files overwrite with unsquashfs

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.

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Vulnerability Analysis

CVE-2020-15229 can be exploited with network access, requires user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have a small impact on confidentiality, a high impact on integrity, and no impact on availability.

Attack Vector:

NETWORK

Attack Complexity:

LOW

Privileges Required:

NONE

User Interaction:

REQUIRED

Scope:

CHANGED

Confidentiality Impact:

LOW

Integrity Impact:

HIGH

Availability Impact:

NONE

Weakness Type

What is a Directory traversal Vulnerability?

The software uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the software does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

CVE-2020-15229 has been classified to as a Directory traversal vulnerability or weakness.

Products Associated with CVE-2020-15229

You can be notified by email with stack.watch whenever vulnerabilities like CVE-2020-15229 are published in these products:

Sylabs Singularity

OpenSuse Leap

OpenSuse Backports Sle

Affected Versions

hpcng singularity Version < 3.6.4 is affected by CVE-2020-15229

Exploit Probability

EPSS

0.88%

Percentile

75.01%

EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.