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FlannelApplication · Flannel Io

CVE-2026-32241

HIGH · 8.8 CVSS v3.1 Published 2026-03-27
Fix available
A fix is available. Upgrade to 0.28.2 or later.
See remediation →
94/100
Remediation priority · Urgent
Remotely reachable Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
Flannel is a network fabric for containers, designed for Kubernetes. The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. In versions of Flannel prior to 0.28.2, this Extension backend is vulnerable to a command injection that allows an attacker who can set Kubernetes Node annotations to achieve root-level arbitrary command execution on every flannel node in the cluster. The Extension backend's SubnetAddCommand and SubnetRemoveCommand receive attacker-controlled data via stdin (from the `flannel.alpha.coreos.com/backend-data` Node annotation). The content of this annotation is unmarshalled and piped directly to a shell command without checks. Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected. The vulnerability is fixed in version v0.28.2. As a workaround, use Flannel with another backend such as vxlan or wireguard.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Flannel's Extension backend (experimental) in versions prior to 0.28.2 contains a command injection vulnerability. The SubnetAddCommand and SubnetRemoveCommand functions receive attacker-controlled data from the flannel.alpha.coreos.com/backend-data Node annotation, unmarshal it, and pipe it directly to a shell command without sanitization, enabling root-level arbitrary command execution on all Flannel nodes using the Extension backend.

MitigationUpgrade Flannel to version 0.28.2 or later to remediate, or alternatively migrate to an unaffected backend such as vxlan or wireguard.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FlannelApplication
Affected:< 0.28.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Determine installed Flannel version
    Run 'flannel --version' or check the Flannel pod image tag in Kubernetes: 'kubectl get pods -n kube-system -l app=flannel -o jsonpath={.items[*].spec.containers[*].image}'
    Affected if Version is below 0.28.2 (e.g., 0.28.1, 0.28.0, 0.27.x, etc.)
  2. Identify which Flannel backend is in use
    Check the Flannel configuration configmap: 'kubectl get configmap -n kube-system flannel-config -o yaml' and inspect the Backend section, or review the 'backend' key in the Flannel manifest file if deployed directly
    Affected if The Backend.Type or Backend.name is set to 'extension' or 'Extension'
  3. Verify Extension backend is actively processing node data
    Query the Node annotation 'flannel.alpha.coreos.com/backend-data' on any node: 'kubectl get nodes -o jsonpath="{.items[*].metadata.annotations.flannel\.alpha\.coreos\.com/backend-data}"'
    Affected if The annotation exists and contains backend data (JSON) that is processed by the Extension backend's SubnetAddCommand or SubnetRemoveCommand functions

User is affected if running Flannel version below 0.28.2 with the Extension backend enabled and the backend-data annotation present on cluster nodes.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 0.28.2 or later
Fixed in 0.28.2
Interim mitigation

Upgrade Flannel to version 0.28.2 or later to remediate, or alternatively migrate to an unaffected backend such as vxlan or wireguard.

Recommended fix High confidence

v0.28.2

  1. Upgrade Flannel to version 0.28.2 or later on all nodes in the cluster
  2. Verify the Flannel DaemonSet or deployment is running the updated version: `kubectl get ds/flannel -n kube-system -o jsonpath='{.spec.template.spec.containers[0].image}'`
  3. Confirm the Extension backend is no longer in use, or if still required, ensure it is running the patched version
  4. Restart Flannel pods if necessary to apply the update: `kubectl rollout restart daemonset/flannel -n kube-system`
  5. Alternatively, if using the Extension backend, migrate to vxlan or wireguard backend by updating the Flannel configuration (e.g., ConfigMap)
Caveat Minimal risk; upgrading to 0.28.2 fixes the command injection. If migrating from Extension to another backend, network configuration changes may be needed.

Generated from the published advisory — verify against the referenced sources before acting.

Fix this in Flannel Scoped from the published advisory
  • Consultation2.0 h
  • Implementation4.0 h
  • Testing3.0 h
  • Review / QA1.0 h
10.0 hours of engineering $1,750
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-32241 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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  • No spam, self-promotion, credentials, or personal data