CVE-2026-32241

Background

The Flannel project includes an experimental Extension backend that allows users to easily prototype new backend types. This backend uses shell commands stored in Kubernetes annotations to configure network connectivity on the node.

Note: consumers are only affected by this vulnerability if they use the experimental Extension backend. Other backends such as vxlan and wireguard are unaffected.

Vulnerability

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.

Workaround

If consumers cannot update to a patched version, then use Flannel with another backend such as vxlan or wireguard.

Credits

Flannel would like to thank Shachar Tal from Palo Alto Networks for reporting this vulnerability.

Kubernetes clusters using Flannel with the Extension backend are affected by this vulnerability. Other backends such as vxlan and wireguard are unaffected.

Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command. Typical impact: arbitrary command execution in the application's environment.

CVE-2026-32241 has a CVSS score of 7.5 (High). The vector is network-reachable, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.28.2); upgrading removes the vulnerable code path.

Kodem intelligence

This is fixed in version v0.28.2.

1. What is CVE-2026-32241? CVE-2026-32241 is a high-severity command injection vulnerability in github.com/flannel-io/flannel (go), affecting versions <= 0.28.1. It is fixed in 0.28.2. Untrusted input is inserted into a command that is later executed by the application, allowing the attacker to alter the intent of that command.
2. How severe is CVE-2026-32241? CVE-2026-32241 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/flannel-io/flannel are affected by CVE-2026-32241? github.com/flannel-io/flannel (go) versions <= 0.28.1 is affected.
4. Is there a fix for CVE-2026-32241? Yes. CVE-2026-32241 is fixed in 0.28.2. Upgrade to this version or later.
5. Is CVE-2026-32241 exploitable, and should I be worried? Whether CVE-2026-32241 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-32241 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-32241? Upgrade github.com/flannel-io/flannel to 0.28.2 or later.