The Helm core maintainers have identified an information disclosure vulnerability in Helm 3.0.0-3.1.2.
Impact
lookup is a Helm template function introduced in Helm v3. It is able to lookup resources in the cluster to check for the existence of specific resources and get details about them. This can be used as part of the process to render templates.
The documented behavior of helm template states that it does not attach to a remote cluster. However, as the recently added lookup template function circumvents this restriction and connects to the cluster even during helm template and helm install|update|delete|rollback --dry-run. The user is not notified of this behavior.
Running helm template should not make calls to a cluster. This is different from install, which is presumed to have access to a cluster in order to load resources into Kubernetes. Helm 2 is unaffected by this vulnerability.
A malicious chart author could inject a lookup into a chart that, when rendered through helm template, performs unannounced lookups against the cluster a user's KUBECONFIG file points to. This information can then be disclosed via the output of helm template.
Patches
This issue has been fixed in Helm 3.2.0
Workarounds
Due to another bug (also fixed in Helm 3.2.0), the command helm lint will fail with an error if the lookup function is used in a chart. Therefore, run helm lint on an untrusted chart before running helm template.
Alternately, setting the KUBECONFIG environment variable to point to an empty Kubernetes configuration file will prevent unintended network connections.
Finally, a chart may be manually analyzed for the presence of a lookup function in any file in the templates/ directory.
For more information
If you have any questions or comments about this advisory:
References
The Helm core maintainers have identified an information disclosure vulnerability in Helm 3.0.0-3.1.2.
Impact
lookupis a Helm template function introduced in Helm v3. It is able to lookup resources in the cluster to check for the existence of specific resources and get details about them. This can be used as part of the process to render templates.The documented behavior of
helm templatestates that it does not attach to a remote cluster. However, as the recently addedlookuptemplate function circumvents this restriction and connects to the cluster even duringhelm templateandhelm install|update|delete|rollback --dry-run. The user is not notified of this behavior.Running
helm templateshould not make calls to a cluster. This is different frominstall, which is presumed to have access to a cluster in order to load resources into Kubernetes. Helm 2 is unaffected by this vulnerability.A malicious chart author could inject a
lookupinto a chart that, when rendered throughhelm template, performs unannounced lookups against the cluster a user'sKUBECONFIGfile points to. This information can then be disclosed via the output ofhelm template.Patches
This issue has been fixed in Helm 3.2.0
Workarounds
Due to another bug (also fixed in Helm 3.2.0), the command
helm lintwill fail with an error if thelookupfunction is used in a chart. Therefore, runhelm linton an untrusted chart before runninghelm template.Alternately, setting the
KUBECONFIGenvironment variable to point to an empty Kubernetes configuration file will prevent unintended network connections.Finally, a chart may be manually analyzed for the presence of a
lookupfunction in any file in thetemplates/directory.For more information
If you have any questions or comments about this advisory:
References