# CVE-2026-63308: Helm denial of service in Files.Lines template helper

Source: https://junglewise.ai/threats/cve-2026-63308-helm-denial-of-service-in-files-lines-template-helper  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-17. Updated: 2026-07-17  
License: CC BY 4.0 with a link back

CVE-2026-63308 · Severity: medium · CVSS 4.3 · Published 2026-07-17

Helm, a popular package manager for Kubernetes, contains a flaw that can cause it to crash when processing certain configuration files. An attacker can provide a specially crafted Helm chart containing an empty file which causes the software to fail during installation, upgrades, or testing. This results in a denial of service where users are unable to deploy or manage their applications using the affected tool.

Technologies: [Helm](https://junglewise.ai/threats/technologies/helm). Vendors: [Helm](https://junglewise.ai/threats/vendors/helm).

## Quick answers

**Is CVE-2026-63308 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-63308 being exploited in the wild.

**How severe is CVE-2026-63308?** Medium severity, with a CVSS score of 4.3, published 17 July 2026.

**Which products and versions are affected?** Helm 3.13.0 through 3.21.0, 4.0.0 through 4.2.3.

**Is there a fix for CVE-2026-63308?** A patch was published on 2026-07-16: Fix merged into main branch Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-63308 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-63308?** Check whether you run Helm at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A denial of service vulnerability exists in Helm's template engine within the `Files.Lines` helper in `pkg/engine/files.go`. The root cause is an improper validation of array indices (CWE-129); specifically, the code checks if a file is nil but fails to check if it is a zero-length byte slice before attempting to access the last character to check for a trailing newline. An attacker can include an empty file in a Helm chart, which triggers an "index out of range [-1]" panic during rendering. This affects `helm template`, `install`, `upgrade`, `lint`, and SDK `Engine.Render` operations. The issue is fixed in commit ba6c9a2 and impacts versions 3.13.0 through 4.2.3.

## Affected products

- Helm Helm 3.13.0 through 3.21.0, 4.0.0 through 4.2.3

## Timeline

- 2026-05-26: disclosed: Vulnerability reported to maintainers via email
- 2026-07-01: other: Public issue opened on GitHub
- 2026-07-16: patched: Fix merged into main branch
- 2026-07-17: advisory: CVE published

## References

- [https://github.com/helm/helm/commit/ba6c9a29efa7bf9198dad6a5ec12b4fb30c96017](https://github.com/helm/helm/commit/ba6c9a29efa7bf9198dad6a5ec12b4fb30c96017)
- [https://github.com/helm/helm/issues/32279](https://github.com/helm/helm/issues/32279)
- [https://github.com/helm/helm/pull/32290](https://github.com/helm/helm/pull/32290)
- [https://www.vulncheck.com/advisories/chat2db-insecure-direct-object-reference-via-get-api-connection-datasource](https://www.vulncheck.com/advisories/chat2db-insecure-direct-object-reference-via-get-api-connection-datasource)

## Related threats

- [Helm path traversal via Chart.yaml name dot-segment](https://junglewise.ai/threats/cve-2026-35206-helm-path-traversal-via-chart-yaml-name-dot-segment)
- [Helm signature verification bypass for plugins missing provenance files](https://junglewise.ai/threats/cve-2026-35205-helm-signature-verification-bypass-for-plugins-missing-provenance)
- [Helm path traversal in plugin metadata version field](https://junglewise.ai/threats/cve-2026-35204-helm-path-traversal-in-plugin-metadata-version-field)