Impact
This issue affects Rancher versions from 2.5.0 up to and including 2.5.16, from 2.6.0 up to and including 2.6.9 and 2.7.0. It only affects Rancher setups that have an external authentication provider configured or had one configured in the past.
It was discovered that when an external authentication provider is configured in Rancher and then disabled, the Rancher generated tokens associated with users who had access granted through the now disabled auth provider are not revoked. This allows users to retain access to Rancher and kubectl access to clusters managed by Rancher, according to their previous configured permissions, even after they are supposed to have lost it due to the auth provider been disabled.
The problem also occurs if the auth provider is configured (and is still enabled) to use the access level scopes allow members of clusters and projects, plus authorized users & groups and restrict access to only the authorized users & groups. In this case, removing users and groups from the authorized lists will not revoke the access tokens and they will remain valid.
An example scenario is:
- OpenLDAP, MS Active Directory (AD) or any other external authentication provider is configured as an auth provider.
- A user (
cluster-owner) is granted cluster-owner permissions on a downstream cluster (test-cluster).
cluster-owner logs in using their external auth provider username and password.cluster-owner generates a kubeconfig token for test-cluster.- The configured external auth provider is disabled.
In this scenario, the kubeconfig generated in step 4 will still be valid after step 5, and test-cluster can still be accessed using the kubeconfig token.
By default, tokens for authenticated session have their ttl (time to live) set to 960 minutes, so they will expire after 16 hours. kubeconfig tokens are configured to never expire, and their ttl is set to 0. These configurations can be changed in the Rancher's settings (Configuration > Global Settings > Settings) with the parameters auth-user-session-ttl-minutes and kubeconfig-default-token-ttl-minutes, respectively.
Workarounds
If you cannot update to a patched Rancher version, the recommended workaround is to review and remove tokens associated with auth providers manually.
The tokens can be reviewed by executing kubectl get tokens in Rancher's local cluster. Each found token must be manually reviewed to check if it belongs to a user from a disabled auth provider or a user who's access was previously removed from the auth provider (when the auth provider is still enabled and is or was configured to use access level scopes, as mentioned above). The identified tokens can be removed with kubectl delete tokens <token_name>.
It is important to mention that this workaround must be done every time an auth provider is disabled in case you cannot update to a patched version.
Patches
Patched versions include releases 2.5.17, 2.6.10, 2.7.1 and later versions. After updating to a patched version, it is highly recommended to review the existing tokens and remove tokens related to disabled auth providers as described above in the workaround section.
For more information
If you have any questions or comments about this advisory:
References
Impact
This issue affects Rancher versions from 2.5.0 up to and including 2.5.16, from 2.6.0 up to and including 2.6.9 and 2.7.0. It only affects Rancher setups that have an external authentication provider configured or had one configured in the past.
It was discovered that when an external authentication provider is configured in Rancher and then disabled, the Rancher generated tokens associated with users who had access granted through the now disabled auth provider are not revoked. This allows users to retain access to Rancher and
kubectlaccess to clusters managed by Rancher, according to their previous configured permissions, even after they are supposed to have lost it due to the auth provider been disabled.The problem also occurs if the auth provider is configured (and is still enabled) to use the access level scopes
allow members of clusters and projects, plus authorized users & groupsandrestrict access to only the authorized users & groups. In this case, removing users and groups from the authorized lists will not revoke the access tokens and they will remain valid.An example scenario is:
cluster-owner) is grantedcluster-ownerpermissions on a downstream cluster (test-cluster).cluster-ownerlogs in using their external auth provider username and password.cluster-ownergenerates akubeconfigtoken fortest-cluster.In this scenario, the
kubeconfiggenerated in step 4 will still be valid after step 5, andtest-clustercan still be accessed using thekubeconfigtoken.By default, tokens for authenticated session have their
ttl(time to live) set to960minutes, so they will expire after16hours.kubeconfigtokens are configured to never expire, and theirttlis set to0. These configurations can be changed in the Rancher's settings (Configuration > Global Settings > Settings) with the parametersauth-user-session-ttl-minutesandkubeconfig-default-token-ttl-minutes, respectively.Workarounds
If you cannot update to a patched Rancher version, the recommended workaround is to review and remove tokens associated with auth providers manually.
The tokens can be reviewed by executing
kubectl get tokensin Rancher'slocalcluster. Each found token must be manually reviewed to check if it belongs to a user from a disabled auth provider or a user who's access was previously removed from the auth provider (when the auth provider is still enabled and is or was configured to use access level scopes, as mentioned above). The identified tokens can be removed withkubectl delete tokens <token_name>.It is important to mention that this workaround must be done every time an auth provider is disabled in case you cannot update to a patched version.
Patches
Patched versions include releases 2.5.17, 2.6.10, 2.7.1 and later versions. After updating to a patched version, it is highly recommended to review the existing tokens and remove tokens related to disabled auth providers as described above in the workaround section.
For more information
If you have any questions or comments about this advisory:
References