CVE-2026-32241

Flannel vulnerable to cross-node remote code execution via extension backend BackendData injection

Published Mar 27, 2026 CVSS 3.1 · 7.5 High EPSS 2.8% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

Source ID Title
Github GHSA Github GHSA GHSA-vchx-5pr6-ffx2 Flannel has cross-node remote code execution via extension backend BackendData injection
History
Type Values Removed Values Added
CPEs cpe:2.3:a:flannel-io:flannel:*:*:*:*:*:kubernetes:*:*
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Flannel-io
Flannel-io flannel
Vendors & Products Flannel-io
Flannel-io flannel
Type Values Removed Values Added
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.
Title Flannel vulnerable to cross-node remote code execution via extension backend BackendData injection
Weaknesses CWE-77
References
Metrics cvssV3_1

{'score': 7.5, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
GitHub_M
Published
Updated
Mar 31, 2026, 6:54 PM
Reserved
Mar 11, 2026, 2:47 PM
Status
Analyzed
Published
Mar 27, 2026, 8:16 PM
Modified
Nov 11, 2026, 11:10 PM