How severe is CVE-2021-32635?

CVE-2021-32635 has a CVSS score of 6.3/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-32635?

CVE-2021-32635 affects the following packages: github.com/sylabs/singularity (Go). Ecosystems affected: Go.

How do I fix CVE-2021-32635?

Update github.com/sylabs/singularity to 3.7.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32635 is resolved across your whole dependency graph.

How do I detect CVE-2021-32635 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sylabs/singularity, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-32635 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-32635 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-32635 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-32635?

CVE-2021-32635 has an EPSS (Exploit Prediction Scoring System) score of 1.4%, placing it in the 73th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-32635?

CVE-2021-32635 is classified as Improper Input Validation (CWE-20), CWE-923 (CWE-923). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-32635 published, and has it been updated?

CVE-2021-32635 was published on May 28, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

MEDIUM severity

CVE-2021-32635 — singularity

MEDIUMFix: sylabs/singularity@d52ae9d

CVE-2021-32635 is a medium-severity (CVSS 6.3) Improper Input Validation vulnerability in github.com/sylabs/singularity. A fix is available for github.com/sylabs/singularity — see the affected versions and patch details below.

Action Commands (run/shell/exec) Against Library URIs Ignore Configured Remote Endpoint

Also known asGHSA-5mv9-q7fq-9394

Published

May 28, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

1.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs73th percentile — riskier than 73% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/sylabs/singularity

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

Due to incorrect use of a default URL, singularity action commands (run/shell/exec) specifying a container using a library:// URI will always attempt to retrieve the container from the default remote endpoint (cloud.sylabs.io) rather than the configured remote endpoint.

An attacker may be able to push a malicious container to the default remote endpoint with a URI that is identical to the URI used by a victim with a non-default remote endpoint, thus executing the malicious container.

Only action commands (run/shell/exec) against library:// URIs are affected. Other commands such as pull / push respect the configured remote endpoint.

Patches

All users should upgrade to Singularity 3.7.4 or later.

A patch was applied at: https://github.com/sylabs/singularity/commit/d52ae9d13979733c5e987a566fae59ed6f1bf796

Workarounds

Users who only interact with the default remote endpoint are not affected.

Installations with an execution control list configured to restrict execution to containers signed with specific secure keys are not affected.

For more information

General questions about the impact of the advisory 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

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/sylabs/singularity`	≥ 3.7.2&&< 3.7.4	3.7.4`go get github.com/sylabs/singularity@v3.7.4`

Affected Products

1 product · 2 configurations

Application

singularitysylabs

2 versions

3.7.23.7.3

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/sylabs/singularity, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/sylabs/singularity to 3.7.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-32635 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

### Impact Due to incorrect use of a default URL, `singularity` action commands (`run`/`shell`/`exec`) specifying a container using a `library://` URI will always attempt to retrieve the container from the default remote endpoint (`cloud.sylabs.io`) rather than the configured remote endpoint. An attacker may be able to push a malicious container to the default remote endpoint with a URI that is identical to the URI used by a victim with a non-default remote endpoint, thus executing the malicious container. Only action commands (`run`/`shell`/`exec`) against `library://` URIs are affected. O