Flux2 is an open and extensible continuous delivery solution for Kubernetes. Flux2 versions between 0.1.0 and 0.29.0, helm-controller 0.1.0 to v0.19.0, and kustomize-controller 0.1.0 to v0.23.0 are vulnerable to Code Injection via malicious Kubeconfig. In multi-tenancy deployments this can also lead to privilege escalation if the controller’s service account has elevated permissions. Workarounds include disabling functionality via Validating Admission webhooks by restricting users from setting the
spec.kubeConfig field in Flux
HelmRelease objects. Additional mitigations include applying restrictive AppArmor and SELinux profiles on the controller’s pod to limit what binaries can be executed. This vulnerability is fixed in kustomize-controller v0.23.0 and helm-controller v0.19.0, both included in flux2 v0.29.0
The software constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.
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When software allows a user’s input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the software. Such an alteration could lead to arbitrary code execution. Injection problems encompass a wide variety of issues – all mitigated in very different ways. For this reason, the most effective way to discuss these weaknesses is to note the distinct features which classify them as injection weaknesses. The most important issue to note is that all injection problems share one thing in common – i.e., they allow for the injection of control plane data into the user-controlled data plane. This means that the execution of the process may be altered by sending code in through legitimate data channels, using no other mechanism. While buffer overflows, and many other flaws, involve the use of some further issue to gain execution, injection problems need only for the data to be parsed. The most classic instantiations of this category of weakness are SQL injection and format string vulnerabilities.