CVE-2025-59823: Gardener Extensions Code Injection RCE Flaw

CVE-2025-59823 Overview

CVE-2025-59823 is a critical code injection vulnerability affecting Project Gardener, an open-source platform that implements automated management and operation of Kubernetes clusters as a service. This vulnerability exists in the Terraformer infrastructure provisioning component used by multiple cloud provider extensions, including AWS, Azure, OpenStack, and GCP providers. Successful exploitation allows a user with administrative privileges for a Gardener project to inject malicious code and gain control over the seed cluster where shoot clusters are managed.

Critical Impact

A privileged attacker can leverage this code injection flaw to compromise the seed cluster, potentially affecting all managed Kubernetes shoot clusters and gaining unauthorized access to cloud infrastructure resources across multiple tenants.

Affected Products

• Gardener Extension for AWS providers prior to version 1.64.0
• Gardener Extension for Azure providers prior to version 1.55.0
• Gardener Extension for OpenStack providers prior to version 1.49.0
• Gardener Extension for GCP providers prior to version 1.46.0

Discovery Timeline

• 2025-09-25 - CVE-2025-59823 published to NVD
• 2025-09-26 - Last updated in NVD database

Technical Details for CVE-2025-59823

Vulnerability Analysis

This vulnerability is classified as CWE-94 (Improper Control of Generation of Code - Code Injection). The flaw resides in how Gardener Extensions process input when utilizing Terraformer for infrastructure provisioning operations. When Terraformer is enabled for managing cloud infrastructure, the affected provider extensions fail to properly sanitize or validate certain inputs, creating an injection point that allows arbitrary code execution.

The attack requires network access with low complexity and needs only low-privilege authentication (administrative access to a Gardener project). What makes this vulnerability particularly severe is its scope-changing nature - successful exploitation allows an attacker to break out of the shoot cluster context and gain control over the seed cluster. Since seed clusters manage multiple shoot clusters, this represents a significant privilege boundary violation that could impact multi-tenant Kubernetes environments.

Root Cause

The root cause stems from improper input validation and sanitization in the Terraformer integration layer within the affected Gardener provider extensions. When processing infrastructure provisioning requests, user-controllable input is incorporated into code execution paths without adequate security controls, enabling code injection attacks. This affects all Gardener installations where Terraformer is used or can be enabled for infrastructure provisioning with any of the vulnerable cloud provider extensions.

Attack Vector

The attack vector is network-based, requiring an authenticated attacker with administrative privileges for a Gardener project. The attacker crafts malicious input during infrastructure provisioning operations that exploits the code injection vulnerability in the Terraformer integration.

The attack flow involves:

1. An attacker with Gardener project admin privileges initiates an infrastructure provisioning operation
2. Malicious payload is injected through the vulnerable input handling mechanism
3. The Terraformer component executes the injected code within the seed cluster context
4. The attacker gains unauthorized access and control over the seed cluster
5. From the compromised seed cluster, the attacker can potentially access other managed shoot clusters

For technical details on the vulnerability mechanism, refer to the GitHub Security Advisory GHSA-227x-7mh8-3cf6.

Detection Methods for CVE-2025-59823

Indicators of Compromise

• Unusual Terraform execution patterns or unexpected infrastructure changes in seed clusters
• Suspicious process spawning or command execution within Gardener extension pods
• Anomalous network connections originating from seed cluster components to unauthorized destinations
• Unexpected modifications to Gardener shoot cluster configurations or credentials

Detection Strategies

• Monitor Gardener extension controller logs for unusual Terraformer execution patterns or error messages indicating injection attempts
• Implement Kubernetes audit logging on seed clusters to detect unauthorized API calls or resource modifications
• Deploy runtime security monitoring (such as SentinelOne Singularity for Cloud) to detect code injection and anomalous process execution in containerized workloads
• Review infrastructure provisioning requests for suspicious or malformed input patterns

Monitoring Recommendations

• Enable comprehensive audit logging for all Gardener seed and shoot cluster operations
• Configure alerts for unexpected Terraform state changes or execution failures
• Monitor container runtime behavior for signs of code injection or privilege escalation
• Implement network segmentation monitoring to detect unauthorized lateral movement from seed clusters

How to Mitigate CVE-2025-59823

Immediate Actions Required

• Upgrade affected Gardener provider extensions immediately to the patched versions
• Audit existing Gardener projects and administrative access to identify potential exposure
• Review seed cluster logs for any signs of prior exploitation
• Consider temporarily disabling Terraformer-based provisioning if immediate patching is not possible

Patch Information

Security patches have been released for all affected Gardener cloud provider extensions:

For detailed security information, see the GitHub Security Advisory GHSA-227x-7mh8-3cf6.

Workarounds

• Restrict administrative access to Gardener projects to only trusted personnel with verified business need
• Implement network policies to limit egress from seed cluster components
• Deploy additional monitoring and alerting on Terraformer execution patterns
• Consider isolating critical seed clusters until patches can be applied

# Example: Verify installed Gardener extension versions
# Check AWS provider extension version
kubectl get deployment -n garden gardener-extension-provider-aws -o jsonpath='{.spec.template.spec.containers[0].image}'

# Check Azure provider extension version
kubectl get deployment -n garden gardener-extension-provider-azure -o jsonpath='{.spec.template.spec.containers[0].image}'

# Check GCP provider extension version
kubectl get deployment -n garden gardener-extension-provider-gcp -o jsonpath='{.spec.template.spec.containers[0].image}'

# Check OpenStack provider extension version
kubectl get deployment -n garden gardener-extension-provider-openstack -o jsonpath='{.spec.template.spec.containers[0].image}'