Improper Neutralization of Special Elements in Output in helm.sh/helm/v3

Exploitation

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

CVSS

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

EPSS

• CVE-2021-21303: 1.09% estimated exploitation activity in the next 30 days; percentile 65.33 (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.

Since Helm 2 was released, a well-documented aspect of Helm is that the Helm chart's version number MUST follow the SemVer2 specification. In the past, Helm would not permit charts with malformed versions. At some point, a patch was merged that changed this - On a version parse error, the version number was simply passed along as-is. This provided a vector for malicious data to be injected into Helm and potentially used in various ways. Core maintainers were able to send deceptive information to a terminal screen running the helm command, as well as obscure or alter information on the screen. In some cases, we could send codes that terminals used to execute higher-order logic, like clearing a terminal screen. Further, during evaluation, the Helm maintainers discovered a few other fields that were not properly sanitized when read out of repository index files. This fix remedies all such cases, and once again enforces SemVer2 policies on version fields. All users of the Helm 3 should…

Published by the source

23 Jun 2021, 18:14 UTC

Last modified by the source

31 May 2024, 16:48 UTC

Source last checked

26 Oct 2026, 15:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-c38g-469g-cmgx

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# Patch Next advisory brief: CVE-2021-21303

Advisory: Improper Neutralization of Special Elements in Output in helm.sh/helm/v3
IDs: CVE-2021-21303, GHSA-c38g-469g-cmgx
Record: https://patchnext.com/advisories/cve-2021-21303 (revision 1, source checked 26 Oct 2026, 15:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: helm.sh/helm/v3 3.5.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go helm.sh/helm/v3: affected >= 3.0.0, < 3.5.2; fixed in 3.5.2

## Suggested inspection (read-only)
- Go helm.sh/helm/v3: 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 helm.sh/helm/v3.
- 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-c38g-469g-cmgx (GitHub-reviewed advisory GHSA-c38g-469g-cmgx lists affected ranges: Go helm.sh/helm/v3 >=3.0.0 <3.5.2)

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