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Vulnerability record · CVE-2021-32635 · published 28 May 2021

CVE-2021-32635: Sylabs singularity improper input validation vulnerability

Sylabs · Singularity

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.

6.3 CVSS 3.1 Medium EPSS 1.4% · top 27.7% CWE-20 · Improper input validationCWE-923 · CWE-923
6.3CVSS 3.1 base score, v2 6.8
1.4%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
6References
17 Jun 2026Last modified by NVD

Description

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.

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

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/sylabs/singularity/releases/tag/v3.7.4 Third Party Advisory
https://github.com/sylabs/singularity/security/advisories/GHSA-5mv9-q7fq-9394 Third Party Advisory
https://security.gentoo.org/glsa/202107-50 Third Party Advisory
https://github.com/sylabs/singularity/releases/tag/v3.7.4 Third Party Advisory
https://github.com/sylabs/singularity/security/advisories/GHSA-5mv9-q7fq-9394 Third Party Advisory
https://security.gentoo.org/glsa/202107-50 Third Party Advisory

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2021-33027Sylabs singularity vulnerabilitySylabs Singularity Enterprise through 1.6.2 has Insufficient Entropy in a nonce.EPSS 1.3%9.8CVE-2021-33622Sylabs singularity vulnerabilitySylabs Singularity 3.5.x and 3.6.x, and SingularityPRO before 3.5-8, has an Incorrect Check of a Function's Return Value.EPSS 1.3%9.3CVE-2020-15229Sylabs singularity path traversal vulnerabilitySingularity (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 …EPSS 2.0%8.8CVE-2020-25040Sylabs singularity exposure of resource to wrong sphere vulnerabilitySylabs Singularity through 3.6.2 has Insecure Permissions on temporary directories used in explicit and implicit container build operations, a differ…EPSS 2.0%8.8CVE-2019-11328Sylabs singularity incorrect permission assignment vulnerabilityAn issue was discovered in Singularity 3.1.0 to 3.2.0-rc2, a malicious user with local/network access to the host system (e.g. ssh) could exploit thi…EPSS 2.1%8.1CVE-2020-25039Sylabs singularity exposure of resource to wrong sphere vulnerabilitySylabs Singularity 3.2.0 through 3.6.2 has Insecure Permissions on temporary directories used in fakeroot or user namespace container execution.EPSS 2.0%7.8CVE-2023-30549Lfprojects apptainer use after free vulnerabilityApptainer is an open source container platform for Linux. There is an ext4 use-after-free flaw that is exploitable through versions of Apptainer < 1.…EPSS 0.37%7.8CVE-2018-19295Sylabs singularity improper input validation vulnerabilitySylabs Singularity 2.4 to 2.6 allows local users to conduct Improper Input Validation attacks.EPSS 0.47%

Source: NIST National Vulnerability Database (record CVE-2021-32635), CISA KEV, FIRST EPSS (scores of 2026-10-19). This page is refreshed as NVD updates the record.