Summary
Insecure permissions on user namespace / fakeroot temporary rootfs in Singularity
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 questions about the impact of the advisory / changes made in the 3.6.0 release can be asked in the:
Any sensitive security concerns should be directed to: [email protected]
See our Security Policy here: https://sylabs.io/security-policy
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.
A file, directory, or other resource is assigned permissions that allow broader access than intended. Typical impact: unauthorized read, modification, or execution of the resource.
CVE-2020-25039 has a CVSS score of 8.1 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.6.3); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
This issue is addressed in Singularity 3.6.3.
All users are advised to upgrade to 3.6.3.
Frequently Asked Questions
- What is CVE-2020-25039? CVE-2020-25039 is a high-severity incorrect permission assignment for critical resource vulnerability in github.com/sylabs/singularity (go), affecting versions >= 3.2.0, < 3.6.3. It is fixed in 3.6.3. A file, directory, or other resource is assigned permissions that allow broader access than intended.
- How severe is CVE-2020-25039? CVE-2020-25039 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of github.com/sylabs/singularity are affected by CVE-2020-25039? github.com/sylabs/singularity (go) versions >= 3.2.0, < 3.6.3 is affected.
- Is there a fix for CVE-2020-25039? Yes. CVE-2020-25039 is fixed in 3.6.3. Upgrade to this version or later.
- Is CVE-2020-25039 exploitable, and should I be worried? Whether CVE-2020-25039 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2020-25039 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2020-25039? Upgrade
github.com/sylabs/singularityto 3.6.3 or later.