CVE-2018-10896 Explained : Impact and Mitigation

In July 2018, a vulnerability was discovered in cloud-init versions starting from 0.6.2, potentially leading to security risks due to shared SSH host keys.

Understanding CVE-2018-10896

What is CVE-2018-10896?

CVE-2018-10896 is a vulnerability in cloud-init versions 0.6.2 and later, where the 'ssh_deletekeys: 0' parameter prevents the deletion of SSH host keys, posing security risks in certain scenarios.

The Impact of CVE-2018-10896

The vulnerability could allow instances created from a central system to share SSH host keys, enabling impersonation or man-in-the-middle attacks.

Technical Details of CVE-2018-10896

Vulnerability Description

In cloud-init 0.6.2 and later, the 'ssh_deletekeys: 0' parameter prevents the deletion of SSH host keys, potentially leading to security risks.

Affected Systems and Versions

Product: cloud-init
Vendor: Canonical
Versions Affected: 0.6.2

Exploitation Mechanism

The vulnerability arises when instances are created by duplicating a central master or template system, causing them to share SSH host keys.

Mitigation and Prevention

Immediate Steps to Take

Update cloud-init to a version where the vulnerability is patched.
Implement unique SSH host keys for each instance to prevent sharing.

Long-Term Security Practices

Regularly update cloud-init and other software to address security vulnerabilities.
Follow best practices for SSH key management to enhance security.

Patching and Updates

Ensure timely patching of cloud-init to the latest version to mitigate the vulnerability.