CVE-2026-32241 in flannel-io flannel

Summary

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.

Responsible

GitHub_M

Reservation

03/11/2026

Disclosure

03/27/2026

Entries

VulDB provides additional information and datapoints for this CVE:

ID	Vulnerability	CWE	Exp	Cou	CVE
354015	flannel-io flannel command injection	77	Not defined	Official fix	CVE-2026-32241