Google Cloud has addressed a medium-severity safety flaw in its platform that might be abused by an attacker who already has entry to a Kubernetes cluster to escalate their privileges.
“An attacker who has compromised the Fluent Bit logging container may mix that entry with excessive privileges required by Anthos Service Mesh (on clusters which have enabled it) to escalate privileges within the cluster,” the corporate mentioned as a part of an advisory launched on December 14, 2023.
Palo Alto Networks Unit 42, which found and reported the shortcoming, mentioned adversaries may weaponize it to hold out “information theft, deploy malicious pods, and disrupt the cluster’s operations.”
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There isn’t a proof that the problem has been exploited within the wild. It has been addressed within the following variations of Google Kubernetes Engine (GKE) and Anthos Service Mesh (ASM) –
- 1.25.16-gke.1020000
- 1.26.10-gke.1235000
- 1.27.7-gke.1293000
- 1.28.4-gke.1083000
- 1.17.8-asm.8
- 1.18.6-asm.2
- 1.19.5-asm.4
A key prerequisite to efficiently exploiting the vulnerability hinges on an attacker having already compromised a FluentBit container by another preliminary entry strategies, comparable to by way of a distant code execution flaw.
“GKE makes use of Fluent Bit to course of logs for workloads operating on clusters,” Google elaborated. “Fluent Bit on GKE was additionally configured to gather logs for Cloud Run workloads. The quantity mount configured to gather these logs gave Fluent Bit entry to Kubernetes service account tokens for different Pods operating on the node.”
This meant {that a} risk actor may use this entry to achieve privileged entry to a Kubernetes cluster that has ASM enabled after which subsequently use ASM’s service account token to escalate their privileges by creating a brand new pod with cluster-admin privileges.
“The clusterrole-aggregation-controller (CRAC) service account might be the main candidate, as it may add arbitrary permissions to present cluster roles,” safety researcher Shaul Ben Hai mentioned. “The attacker can replace the cluster function certain to CRAC to own all privileges.”
By means of fixes, Google has eliminated Fluent Bit’s entry to the service account tokens and re-architected the performance of ASM to take away extreme role-based entry management (RBAC) permissions.
“Cloud distributors routinely create system pods when your cluster is launched,” Ben Hai concluded. “They’re in-built your Kubernetes infrastructure, the identical as add-on pods which were created whenever you allow a characteristic.”
“It is because cloud or software distributors sometimes create and handle them, and the consumer has no management over their configuration or permissions. This may also be extraordinarily dangerous since these pods run with elevated privileges.”
