CVE-2025-47282: Gardener DNS Privilege Escalation Flaw

CVE-2025-47282 Overview

A critical privilege escalation vulnerability has been discovered in Gardener External DNS Management, a Kubernetes extension used to manage external DNS entries for clusters. This security flaw allows users with administrative privileges for a Gardener project or a shoot cluster (including administrative privileges for a single namespace of the shoot cluster) to obtain control over the seed cluster where the shoot cluster is managed.

This vulnerability is classified as an Improper Input Validation (CWE-20) issue and affects all Gardener installations regardless of the public cloud provider(s) used for seed clusters or shoot clusters. The severity of this vulnerability is amplified by the cross-scope impact, where compromising a shoot cluster can lead to full control of the seed cluster infrastructure.

Critical Impact

Attackers with limited administrative access to Gardener projects or shoot clusters can escalate privileges to gain full control over seed clusters, potentially compromising the entire Kubernetes infrastructure management plane.

Affected Products

• Gardener External DNS Management versions prior to 0.23.6
• Gardener Extension Shoot DNS Service versions <= v1.60.0 (when the external-dns-management component is deployed on seeds)
• All Gardener installations using the affected gardener/external-dns-management component

Discovery Timeline

• 2025-05-19 - CVE-2025-47282 published to NVD
• 2025-05-21 - Last updated in NVD database

Technical Details for CVE-2025-47282

Vulnerability Analysis

The vulnerability exists in the gardener/external-dns-management component, which is responsible for managing external DNS entries within Kubernetes clusters. The improper input validation flaw allows authenticated users with limited administrative scope to escape their intended privilege boundaries.

In Gardener's architecture, seed clusters are the management layer that host the control planes of multiple shoot clusters (workload clusters). The hierarchical trust model assumes that shoot cluster administrators should not have access to the underlying seed cluster infrastructure. This vulnerability breaks that isolation boundary.

The attack is particularly concerning because it can be triggered by users who only have namespace-level administrative privileges within a shoot cluster, making it accessible to a relatively wide range of authenticated users.

Root Cause

The root cause is improper input validation (CWE-20) in the gardener/external-dns-management component. The component fails to properly validate or sanitize inputs from shoot cluster administrators, allowing them to craft malicious inputs that can affect the seed cluster context.

The external-dns-management component may be deployed on seed clusters either directly or through the gardener/gardener-extension-shoot-dns-service extension. In both deployment scenarios, the vulnerable code path can be triggered by users with shoot-level administrative access.

Attack Vector

The attack is network-based and requires low privileges (authenticated access with administrative privileges for a Gardener project, shoot cluster, or even a single namespace within a shoot cluster). The attack does not require user interaction and has a changed scope, meaning the vulnerable component impacts resources beyond its security scope.

An attacker would leverage their legitimate administrative access to a shoot cluster to craft malicious DNS management requests. These requests exploit the improper input validation to execute operations in the context of the seed cluster, effectively escalating from shoot-level to seed-level privileges.

Detection Methods for CVE-2025-47282

Indicators of Compromise

• Unexpected DNS entries or modifications originating from shoot cluster namespaces
• Anomalous API calls to the external-dns-management component from shoot cluster service accounts
• Unauthorized access attempts or successful authentications to seed cluster resources from shoot cluster contexts
• Unusual resource creation or modification events in seed clusters correlated with shoot cluster administrative actions

Detection Strategies

• Monitor Kubernetes audit logs for cross-namespace or cross-cluster resource access patterns involving DNS management components
• Implement alerting for any seed cluster modifications initiated from shoot cluster contexts
• Track version information for external-dns-management and shoot-dns-service components across all clusters
• Review RBAC bindings and service account permissions for unexpected privilege grants

Monitoring Recommendations

• Enable detailed audit logging for all Gardener components, particularly external-dns-management and related extensions
• Set up alerts for privilege escalation patterns between shoot and seed cluster boundaries
• Monitor for unexpected service account token usage or cross-cluster authentication events
• Regularly audit deployed component versions against known vulnerable versions

How to Mitigate CVE-2025-47282

Immediate Actions Required

• Upgrade gardener/external-dns-management to version 0.23.6 or later immediately
• Update gardener/gardener-extension-shoot-dns-service to a version greater than v1.60.0 if the extension is enabled
• Review audit logs for any suspicious activity that may indicate prior exploitation
• Temporarily restrict administrative access to Gardener projects and shoot clusters to essential personnel only

Patch Information

The vulnerability has been fixed in Gardener External DNS Management version 0.23.6. For environments using the shoot-dns-service extension, ensure you are using a version greater than v1.60.0. The GitHub Security Advisory provides additional details about the fix.

Workarounds

• If immediate patching is not possible, consider temporarily disabling the external-dns-management component or the shoot-dns-service extension where feasible
• Implement strict network policies to limit communication between shoot and seed cluster components
• Enforce additional authentication and authorization checks at the seed cluster boundary
• Review and minimize administrative privileges granted to Gardener projects and shoot cluster users