CVE-2025-7342: Kubernetes Image Builder Privilege Escalation

CVE-2025-7342 Overview

A security vulnerability was discovered in the Kubernetes Image Builder where default credentials are enabled during the Windows image build process when using the Nutanix or VMware OVA providers. These credentials, which allow root access, are disabled at the conclusion of the build. Kubernetes clusters are only affected if their nodes use VM images created via the Image Builder project and the vulnerability was exploited during the build process, which requires an attacker to access the build VM and modify the image while the build is in progress.

Critical Impact

This hardcoded credentials vulnerability (CWE-798) could allow an attacker with network access during the image build process to gain root-level access to Windows VM images, potentially compromising all Kubernetes cluster nodes using those images.

Affected Products

• Kubernetes Image Builder (Windows image builds)
• Nutanix provider for Kubernetes Image Builder
• VMware OVA provider for Kubernetes Image Builder

Discovery Timeline

• August 17, 2025 - CVE-2025-7342 published to NVD
• November 4, 2025 - Last updated in NVD database

Technical Details for CVE-2025-7342

Vulnerability Analysis

This vulnerability falls under CWE-798 (Use of Hard-coded Credentials), a significant security concern in infrastructure automation tooling. The Kubernetes Image Builder employs default credentials during the Windows image build process to facilitate automated configuration and provisioning steps. While these credentials are intended to be temporary and are disabled at the conclusion of the build process, the window of exposure during active builds creates an exploitable attack surface.

The exploitation requires network access to the build VM during the image creation process. An attacker who successfully accesses the build environment can leverage the default credentials to gain root-level access, allowing them to modify the image before it is finalized. Any Kubernetes cluster subsequently deploying nodes from a compromised image would inherit the malicious modifications.

Root Cause

The root cause stems from the use of hardcoded default credentials in the Image Builder's Windows image build workflow for Nutanix and VMware OVA providers. While this approach simplifies the automated build process, it creates a time-of-check to time-of-use (TOCTOU) style vulnerability where the credentials remain active and exploitable during the entire build duration. The security assumption that the build environment is isolated and trusted may not hold in all deployment scenarios.

Attack Vector

The attack vector is network-based, requiring the attacker to gain access to the build VM during the active image build process. This represents a constrained attack window, as the vulnerability is only exploitable while the build is in progress and the default credentials are active. Successful exploitation requires:

1. Network visibility to the build VM environment
2. Timing the attack during an active Windows image build
3. Using the default credentials to authenticate to the build VM
4. Modifying the image or implanting persistent access mechanisms before the build concludes

The vulnerability requires no privileges on the target system but does require user interaction in the form of an administrator initiating an image build process.

Detection Methods for CVE-2025-7342

Indicators of Compromise

• Unexpected network connections to build VMs during image creation processes
• Authentication attempts using default or well-known credentials against Image Builder infrastructure
• Unauthorized modifications to VM images or templates in Nutanix or VMware environments
• Anomalous process execution or file system changes on build VMs during active builds

Detection Strategies

• Monitor network traffic to and from Kubernetes Image Builder VMs for suspicious connection patterns
• Implement audit logging for all authentication events on build infrastructure
• Deploy file integrity monitoring on build VMs to detect unauthorized image modifications
• Review VMware and Nutanix logs for access anomalies during image build windows

Monitoring Recommendations

• Enable verbose logging for the Kubernetes Image Builder process
• Configure alerts for any authentication attempts to build VMs from unexpected source IPs
• Implement network segmentation monitoring to detect lateral movement toward build infrastructure
• Establish baseline metrics for image build duration and flag builds that exceed normal parameters

How to Mitigate CVE-2025-7342

Immediate Actions Required

• Isolate Kubernetes Image Builder environments from untrusted networks during build operations
• Audit all Windows VM images previously built using Nutanix or VMware OVA providers for signs of compromise
• Implement network segmentation to restrict access to build VMs during the image creation process
• Review and rotate any credentials associated with the Image Builder infrastructure

Patch Information

Organizations should consult the official Kubernetes security resources for updated Image Builder versions that address this vulnerability. Additional details are available through the Kubernetes Security Announcement and the GitHub Issue Discussion. The OSS Security Mailing List also contains relevant disclosure information.

Workarounds

• Build images only in fully isolated network environments with no external connectivity
• Implement strict firewall rules to block all inbound connections to build VMs except from trusted management hosts
• Use jump hosts or bastion servers with multi-factor authentication for any required access to the build environment
• Consider implementing just-in-time (JIT) access controls for build infrastructure access

# Example network isolation configuration for build environment
# Restrict inbound access to build VMs during image creation

# Block all inbound traffic to build VM network segment
iptables -A INPUT -d 10.0.100.0/24 -j DROP

# Allow only from trusted management subnet
iptables -I INPUT -s 10.0.50.0/24 -d 10.0.100.0/24 -j ACCEPT

# Log any blocked connection attempts for monitoring
iptables -I INPUT -d 10.0.100.0/24 -j LOG --log-prefix "BUILD-VM-BLOCKED: "