CVE-2025-7342

Executive Summary

CVE-2025-7342 is a security advisory affecting the Kubernetes Image Builder project. The vulnerability involves default credentials being enabled during the Windows image build process when using the Nutanix or VMware OVA providers. These credentials, which grant root-level access, are intended to be disabled at the conclusion of the build. However, an attacker with access to the build VM during the build process could exploit these credentials to modify the resulting VM image, potentially compromising all nodes created from that image. The CVSS score is 7.5 (High), with a local attack vector and low attack complexity. No public proof-of-concept or exploit code is available, and the EPSS score is 0.0%, indicating very low exploitation likelihood at this time. The vendor has not yet released a patch.

Supply Chain & Package Security

This vulnerability is not related to NPM, PyPI, Go, or Ruby packages. It is specific to the Kubernetes Image Builder project, which is used to create VM images for Kubernetes nodes. The risk is primarily to organizations that use the Image Builder with Nutanix or VMware OVA providers to create Windows-based VM images. An attacker who compromises the build pipeline could inject malicious code into the resulting images, affecting the entire Kubernetes cluster.

CVSS Breakdown & Threat Level

• CVSS Score: 7.5 (High)
• Attack Vector: Local (AV:L) – The attacker must have access to the build VM.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: None (PR:N) – No privileges needed to exploit the default credentials.
• User Interaction: None (UI:N) – No user action required.
• Scope: Unchanged (S:U) – The vulnerability does not affect other components.
• Confidentiality Impact: High (C:H) – Full access to the image and its data.
• Integrity Impact: High (I:H) – Ability to modify the image.
• Availability Impact: High (A:H) – Could lead to denial of service or malicious modifications.

Threat Level: High. While the attack vector is local, the potential impact on the supply chain and the Kubernetes cluster is severe. The lack of a patch increases the risk for organizations using the affected providers.

Deep Dive & Mechanics

The Kubernetes Image Builder is a tool used to create custom VM images for Kubernetes nodes. It supports multiple providers, including Nutanix and VMware OVA. During the Windows image build process, the tool enables default credentials (e.g., a default username and password) to allow the build process to access the VM. These credentials are intended to be disabled at the end of the build. However, if an attacker gains access to the build VM while the build is in progress, they can use these credentials to log in and modify the image. This could include installing backdoors, altering configurations, or injecting malware. The resulting compromised image would then be used to create Kubernetes nodes, giving the attacker persistent access to the cluster.

The vulnerability is not exploitable after the build is complete, as the credentials are disabled. However, the build process itself is a critical point of failure. Attackers could exploit this by compromising the build environment, such as through a compromised CI/CD pipeline, insider threat, or network access to the build VM.

Vulnerable vs. Patched Code

No specific code snippets are available for this vulnerability. The issue is a configuration flaw in the Image Builder's build scripts for Windows images when using Nutanix or VMware OVA providers. The vulnerable behavior is the enabling of default credentials during the build. A patched version would either not enable these credentials or would use stronger, temporary credentials that are rotated during the build. Since no patch is available, the exact code changes are unknown.

Exploitation & Lab Setup

Red Team

Objective: Simulate an attacker with access to the build VM during the Windows image build process.

Lab Setup:

1. Set up a Kubernetes Image Builder environment with the Nutanix or VMware OVA provider.
2. Initiate a Windows image build.
3. During the build, gain access to the build VM (e.g., via SSH or console).
4. Use the default credentials (e.g., username: Administrator, password: password) to log in.
5. Modify the image, such as adding a backdoor user or installing a reverse shell.
6. Complete the build and deploy the compromised image to a Kubernetes cluster.

Example Command (Linux):

# Assuming access to the build VM
ssh Administrator@<build-vm-ip>
# Modify the image (e.g., add a user)
net user attacker Password123! /add
net localgroup Administrators attacker /add

Blue Team

Objective: Detect and prevent exploitation of this vulnerability.

Detection:

• Monitor build VMs for unexpected SSH or RDP connections during the build process.
• Alert on the use of default credentials (e.g., login attempts with Administrator and common passwords).
• Monitor for modifications to the image files during the build (e.g., file integrity monitoring).

Prevention:

• Isolate the build environment from untrusted networks.
• Use strong, temporary credentials that are rotated during the build.
• Implement strict access controls to the build VM.
• Use a secure build pipeline with integrity checks.

Indicators of Compromise (IOCs)

• Network: Unusual SSH or RDP connections to build VMs during the build process.
• Host: Login events with default usernames (e.g., Administrator) and common passwords.
• File: Modifications to the VM image files (e.g., .vmdk, .ova) during the build.
• Process: Unexpected processes running on the build VM (e.g., backdoor shells).
• Log: Windows Event ID 4625 (failed logon) or 4624 (successful logon) with default credentials.

Detection Engineering

YARA Rule

rule CVE_2025_7342_Default_Credentials {
    meta:
        description = "Detects default credentials in Kubernetes Image Builder Windows builds"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-7342"
    strings:
        $cred1 = "Administrator" ascii wide nocase
        $cred2 = "password" ascii wide nocase
        $cred3 = "default" ascii wide nocase
    condition:
        any of ($cred*) and filesize < 10MB
}

Sigma Rule

title: CVE-2025-7342 - Default Credentials Used During Kubernetes Image Builder Build
id: 8a9b3c4d-5e6f-7a8b-9c0d-1e2f3a4b5c6d
status: experimental
description: Detects login attempts with default credentials on build VMs during Windows image build
author: Valters IT
date: 2025-04-10
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2025-7342
logsource:
    product: windows
    service: security
detection:
    selection:
        EventID: 4624
        AccountName: 'Administrator'
        LogonType: 3
    condition: selection
falsepositives:
    - Legitimate build processes using default credentials (should be disabled)
level: high

Suricata Rule

alert tcp $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-7342 - Default Credentials Attempt on Build VM"; flow:to_server,established; content:"Administrator"; nocase; content:"password"; nocase; distance:0; within:100; classtype:attempted-admin; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Isolate Build Environment: Ensure the build VM is not accessible from untrusted networks.
2. Use Strong Credentials: If possible, modify the build scripts to use strong, temporary credentials that are rotated during the build.
3. Monitor Build Process: Implement logging and monitoring for any unauthorized access to the build VM.
4. Review Image Integrity: After the build, verify the integrity of the resulting image (e.g., checksums, signatures).

Long-Term Fix:

• Wait for an official patch from the Kubernetes Image Builder project. The patch should disable default credentials during the build or use a more secure authentication mechanism.
• Consider using alternative image building methods that do not rely on default credentials.

Workaround:

• If using Nutanix or VMware OVA providers, manually disable default credentials in the build scripts or use a different provider.

Valters IT
DevSecOps & Cyber Threat Intelligence Expert