Google Cloud acted promptly to rectify a significant security vulnerability in its platform, focusing on a medium-severity flaw that could enable an attacker, already possessing access to a Kubernetes cluster, to elevate their privileges. Discovered by Palo Alto Networks Unit 42, this loophole exploited the Fluent Bit logging container, potentially granting unauthorized access to Anthos Service Mesh (ASM) high privileges within the affected clusters.
The flaw, disclosed on December 14, 2023, highlighted the risks of combining compromised access with heightened permissions, potentially leading to data theft, malicious pod deployment, and cluster disruption. Although there’s no evidence of exploitation in the wild, Google Cloud swiftly addressed the issue by rolling out fixes in specified versions of Google Kubernetes Engine (GKE) and Anthos Service Mesh (ASM).
The affected versions, ranging from 1.25.16-gke.1020000 to 1.28.4-gke.1083000 for GKE and 1.17.8-asm.8 to 1.19.5-asm.4 for ASM, received updates to mitigate this vulnerability’s impact. The fix aimed to curb the escalation of privileges by reconfiguring Fluent Bit’s access to service account tokens and re-architecting ASM functionalities, limiting excessive role-based access control (RBAC) permissions.
The vulnerability’s exploitation was contingent on an attacker already having breached a Fluent Bit container through initial access methods, like remote code execution vulnerabilities. The breach allowed access to Kubernetes service account tokens, leading to potential escalation of privileges within a cluster with enabled Anthos Service Mesh.
This incident emphasizes the critical need for securing initial access points to prevent subsequent cluster compromise and highlights the complex nature of cloud infrastructure’s inherent risks, particularly regarding add-on and system pods’ elevated privileges in Kubernetes infrastructure.