Google LLC has patched two significant vulnerabilities in Google Kubernetes Engine that could allow an attacker to gain control of a Kubernetes cluster.

The vulnerabilities, detailed Dec. 27 by researchers at Palo Alto Network Inc.’s Unit 42, involved an issue in the default configuration of GKE’s logging agent FluentBit, which runs by default on all clusters and the default privileges for Anthos Service Mesh, an option add-on that customers can enable.

By themselves, the vulnerabilities cause no major risk, but when both are exploited, an attacker can exploit GKE. To exploit the pair of vulnerabilities, an attacker must first execute in the FluentBit container and if the cluster also has ASM installed, they can create a powerful chain to gain control of a Kubernetes cluster.

A misconfiguration in FluentBit allows an attacker to execute code in the FluentBit container to access sensitive tokens from other pods, enabling unauthorized actions in the cluster. ASM’s Container Network Interface DaemonSet retains excessive permissions even after installation, allowing an attack to create new pods with extensive permissions, further escalating the attacker’s control over the cluster.

The combination of the vulnerabilities allows an attacker to gain control of the FluentBit container, access other pods’ tokens, create new pods with high privileges and ultimately gain administrative control over the entire Kubernetes cluster.

The good news is that Google addressed both vulnerabilities through GCP-2023-047, with a patch released on Dec. 14, but as with all things cybersecurity, a patch only works when it’s applied. And the patch for the ASM vulnerability can only be applied manually.

The form of attack, a tandem or chain vulnerability, has security experts expressing concern.

“In complex systems like Kubernetes, it is not uncommon to find vulnerabilities that can be exploited in tandem,” Callie Guenther, senior manager of Cyber Threat Research at managed detection and response company Critical Start Inc., told SiliconANGLE today. “However, it’s less common for two distinct vulnerabilities in different components (like FluentBit and ASM in this case) to align in a way that allows for such a significant escalation of privileges.”

The ability to escalate privileges and potentially take over an entire Kubernetes cluster is quite serious, Guenther explained. “Kubernetes clusters often run critical applications and services and a takeover could lead to significant operational disruptions, data theft or deployment of malicious applications,” she said.

Joseph Carson, chief security scientist and advisory chief information security officer at privileged access management firm Delinea Inc., said chaining vulnerabilities is a common technique that more advanced and sophisticated attackers use to access victims’ environments.

“These types of vulnerabilities make it difficult for organizations to evaluate the risks as they might look at each vulnerability individually,” Carson said. “This is why organizations must assess the risks of the service as a whole and identify vulnerability chain exploits that they might be exposed to.”

Image: Google