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GHSA-vvmq-fwmg-2gjc
No affected components available
Flux2 can reconcile the state of a remote cluster when provided with a kubeconfig with the correct access rights. Kubeconfig files can define commands to be executed to generate on-demand authentication tokens. A malicious user with write access to a Flux source or direct access to the target cluster, could craft a kubeconfig to execute arbitrary code inside the controller’s container.
In multi-tenancy deployments this can also lead to privilege escalation if the controller's service account has elevated permissions.
Impact
Within the affected versions range, one of the permissions set below would be required for the vulnerability to be exploited:
- Direct access to the cluster to create Flux
KustomizationorHelmReleaseobjects and Kubernetes Secrets. - Direct access to the cluster to modify existing Kubernetes secrets being used as
kubeconfigin existing FluxKustomizationorHelmReleaseobjects. - Direct access to the cluster to modify existing Flux
KustomizationorHelmReleaseobjects and access to create or modify existing Kubernetes secrets. - Access rights to make changes to a configured Flux Source (i.e. Git repository).
Patches
This vulnerability was fixed in kustomize-controller v0.23.0 and helm-controller v0.19.0, both included in flux2 v0.29.0. Starting from the fixed versions, both controllers disable the use of command execution from kubeconfig files by default, users have to opt-in by adding the flag --insecure-kubeconfig-exec to the controller’s command arguments. Users are no longer allowed to refer to files in the controller’s filesystem in the kubeconfig files provided for the remote apply feature.
Workarounds
- The functionality can be disabled via Validating Admission webhooks (e.g. OPA Gatekeeper, Kyverno) by restricting users from being able to set the
spec.kubeConfigfield in FluxKustomizationandHelmReleaseobjects. - Applying restrictive AppArmor and SELinux profiles on the controller’s pod to limit what binaries can be executed.
Credits
The Flux engineering team found and patched this vulnerability.
For more information
If you have any questions or comments about this advisory please open an issue in the flux2 repository.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker needs basic access or low-level privileges. No user interaction is needed for the attacker to exploit this vulnerability. The vulnerability can affect other systems as well, not just the initial system. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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