dbcve.org
SingularityApplication · Sylabs

CVE-2021-32635

MEDIUM · 6.3 CVSS v3.1 Published 2021-05-28
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
70/100
Remediation priority · Elevated
Remotely reachable No privileges

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Singularity is an open source container platform. In verions 3.7.2 and 3.7.3, Dde 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. The vulnerability is patched in Singularity version 3.7.4. Two possible workarounds exist: Users can only interact with the default remote endpoint, or an installation can have an execution control list configured to restrict execution to containers signed with specific secure keys.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

In Singularity 3.7.2 and 3.7.3, the `library://` URI scheme used with action commands (run/shell/exec) always connects to the default remote endpoint (cloud.sylabs.io) regardless of the user's configured remote endpoint. An attacker who knows the URI a victim would request can push a malicious container to the default endpoint, which will then be executed instead of the container from the victim's intended non-default endpoint.

MitigationUpgrade to Singularity 3.7.4 or later, or alternatively restrict interactions to the default remote endpoint or configure an execution control list (ECL) to only allow containers signed with trusted keys.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
SingularityApplication
Affected:= 3.7.2= 3.7.3

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Scope
Unchanged
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Singularity version
    Run `singularity --version` or `singularity version` to determine the installed version number
    Affected if Version is 3.7.2 or 3.7.3 specifically (exact match to affected versions)
  2. List configured remote endpoints
    Run `singularity remote list` to see all configured remote endpoints
    Affected if More than one remote is listed, or a non-default remote is set as active (indicates custom remote configuration)
  3. Check active remote endpoint
    Run `singularity remote list` and look for the entry marked with an asterisk or '(default)' - this shows which remote is currently active
    Affected if A non-default remote is marked as active (not cloud.sylabs.io) - the user has configured and is using a different endpoint than the default
  4. Identify usage of library:// URI scheme
    Review command history or scripts for any `singularity run/shell/exec library://` commands that pull containers from the library URI scheme
    Affected if The user has run or intends to run containers using the `library://` URI scheme while using a non-default remote configuration

User is affected if Singularity version is exactly 3.7.2 or 3.7.3 AND they have configured a non-default remote endpoint AND they use the library:// URI scheme with action commands (run/shell/exec). If any of these conditions are false, the vulnerability does not apply.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to Singularity 3.7.4 or later, or alternatively restrict interactions to the default remote endpoint or configure an execution control list (ECL) to only allow containers signed with trusted keys.

Fix this in Singularity Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing2.0 h
5.0 hours of engineering $880
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-32635 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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