CVE-2022-39272 - Flux DoS Vulnerability Explained with Simple Code Example & Mitigation

Flux is one of the most popular open and extensible continuous delivery (CD) tools for Kubernetes. It automates the management of your Kubernetes clusters and continuously applies configurations based on your code repositories. However, before version .35., Flux had a serious security issue—CVE-2022-39272—that could let attackers (or even mistake-prone users) *knock out* whole resource types using a simple YAML misconfiguration.

This article explains what happened, demonstrates a real-world example, and shows you how to defend your clusters—using plain, simple language.

What is CVE-2022-39272?

In short: If someone can mess with certain fields of a Flux CD-controlled object (particularly .spec.interval or .spec.timeout), supplying them with invalid values, they can cause an internal error powerful enough to break processing of ALL objects of that type in the cluster—not just the one they tweaked.

Think of it like a simple typo taking down an entire department at work! This is a form of Denial of Service (DoS), so it’s a big deal.

References

- GitHub Security Advisory for Flux, CVE-2022-39272
- NVD Entry
- Flux v.35. Release Notes (fixing bug)

Who is Vulnerable?

Any Kubernetes cluster using Flux CD versions below v.35. is exposed. If your users (or attackers) have permission to apply or edit Flux custom resources (like GitRepository, Kustomization, etc.), this affects you.

Flux objects like this

apiVersion: source.toolkit.fluxcd.io/v1beta1
kind: GitRepository
metadata:
  name: my-repo
spec:
  interval: 10ms
  timeout: 1ms
  # ...other fields...

The .spec.interval and .spec.timeout fields are supposed to have values like 1ms (1 minute), 30s (30 seconds), etc. If someone puts in invalid data (like a string that doesn’t make sense), Flux would hit a runtime error while parsing the value, and the *entire controller* for that type (e.g., all GitRepository objects) would crash, so nothing would get processed until it’s fixed.

Exploit Example

Let’s say an attacker wants to intentionally disrupt your GitOps workflow, or a developer accidentally pastes the wrong value.

Here’s a malicious—or just erroneous—YAML

apiVersion: source.toolkit.fluxcd.io/v1beta1
kind: GitRepository
metadata:
  name: evil-repo
spec:
  interval: "not-a-time"
  timeout: ""

This value "not-a-time" is NOT a valid interval. When Flux tries to parse this object, it will panic, and then stop processing ALL GitRepository resources—not just the bad one.

What does this mean? Your whole pipeline grinds to a halt for that resource type. Code stops being deployed. Configuration drift can go undetected.

Typical error messages in Flux controller logs would look like

panic: time: invalid duration "not-a-time"

Or similar; after this, the controller restarts, but repeatedly encounters the fatal parsing error and never makes progress until the bad object is fixed.

1. THE Right Way: Upgrade Flux

Upgrade Flux to v.35. or later, where this bug is patched and malformed intervals are properly handled *without taking down entire controllers*.

flux --version
# → upgrade if below .35.!

Use your normal upgrade path (Helm, manifests, etc.)

2. Workaround: Admission Controller

If you can’t upgrade Flux right away, use Kubernetes admission controllers (like OPA Gatekeeper or Kyverno) to block invalid .spec.interval and .spec.timeout values.

Example OPA ConstraintTemplate

apiVersion: templates.gatekeeper.sh/v1beta1
kind: ConstraintTemplate
metadata:
  name: fluxintervals
spec:
  crd:
    spec:
      names:
        kind: FluxIntervalConstraint
  targets:
    - target: admission.k8s.gatekeeper.sh
      rego: |
        package fluxcd

        violation[{"msg": msg}] {
          input.review.object.spec.interval != ""
          not regex.match("^[-9]+[smh]$", input.review.object.spec.interval)
          msg := sprintf("Invalid .spec.interval: %v", [input.review.object.spec.interval])
        }

You’d then create a Constraint to enforce it on relevant resources.

Summary Table

| Risk | Flux <= .34.x | Flux >= .35. |
|--------------------------|------------------------|---------------------|
| DoS via invalid interval | Vulnerable | Safe |
| Mitigation needed | Yes (controller) | No |

Patch your Flux now! Anything before .35. is not safe.

- If you can’t upgrade, enforce strict .spec.interval and .spec.timeout values with an admission controller.

Stay safe and happy shipping 🚢!

If you have further questions or need expert help securing your CD pipeline, consult the official Flux documentation or drop by their GitHub discussions board.

Timeline

Published on: 10/22/2022 00:15:00 UTC
Last modified on: 10/24/2022 16:51:00 UTC