Insecure permissions on user namespace / fakeroot temporary rootfs in Singularity

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.1 · CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

EPSS

• CVE-2020-25039: 2.01% estimated exploitation activity in the next 30 days; percentile 80.92 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Impact Insecure permissions on temporary directories used in fakeroot or user namespace container execution. When a Singularity action command (run, shell, exec) is run with the fakeroot or user namespace option, Singularity will extract a container image to a temporary sandbox directory. Due to insecure permissions on the temporary directory it is possible for any user with access to the system to read the contents of the image. Additionally, if the image contains a world-writable file or directory, it is possible for a user to inject arbitrary content into the running container. Patches This issue is addressed in Singularity 3.6.3. All users are advised to upgrade to 3.6.3. Workarounds The issue is mitigated if TMPDIR is set to a location that is only accessible to the user, as any subdirectories directly under TMPDIR cannot then be accessed by others. However, this is difficult to enforce so it is not recommended to rely on this as a mitigation. For more information General…

Published by the source

20 Dec 2021, 18:25 UTC

Last modified by the source

1 Feb 2023, 05:05 UTC

Source last checked

26 Oct 2026, 14:54 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-w6v2-qchm-grj7

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# Patch Next advisory brief: CVE-2020-25039

Advisory: Insecure permissions on user namespace / fakeroot temporary rootfs in Singularity
IDs: CVE-2020-25039, GHSA-w6v2-qchm-grj7
Record: https://patchnext.com/advisories/cve-2020-25039 (revision 1, source checked 26 Oct 2026, 14:54 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/sylabs/singularity 3.6.3. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/sylabs/singularity: affected >= 3.2.0, < 3.6.3; fixed in 3.6.3

## Suggested inspection (read-only)
- Go github.com/sylabs/singularity: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/sylabs/singularity.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w6v2-qchm-grj7 (GitHub-reviewed advisory GHSA-w6v2-qchm-grj7 lists affected ranges: Go github.com/sylabs/singularity >=3.2.0 <3.6.3)

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