CVE-2021-32726 Explained : Impact and Mitigation

A high-severity vulnerability, CVE-2021-32726, in Nextcloud Server versions prior to 19.0.13, 20.0.11, and 21.0.3 allowed unauthorized access due to webauthn tokens not being deleted after a user's deletion.

Understanding CVE-2021-32726

This section provides insights into the impact and technical details of the CVE.

What is CVE-2021-32726?

Nextcloud Server's versions before 19.0.13, 20.0.11, and 21.0.3 failed to delete webauthn tokens after user deletion, enabling previous users to gain unauthorized access by reusing usernames.

The Impact of CVE-2021-32726

The vulnerability received a CVSS score of 7.1, indicating a high severity with confidentiality, integrity, and availability impacts. Attack complexity is high with network-based attack vectors.

Technical Details of CVE-2021-32726

This section delves into the vulnerability description, affected systems, and exploitation mechanism.

Vulnerability Description

Webauthn tokens were retained post-user deletion, enabling illicit access upon username reuse, posing a security threat to Nextcloud Server instances.

Affected Systems and Versions

Nextcloud Server versions below 19.0.13, 20.0.11, and 21.0.3 were susceptible to the persistence of webauthn tokens, potentially leading to unauthorized access.

Exploitation Mechanism

Malicious actors could exploit the retained webauthn tokens to gain access to user accounts by leveraging previously used usernames, highlighting a critical security flaw.

Mitigation and Prevention

Discover steps to mitigate and prevent the exploitation of CVE-2021-32726.

Immediate Steps to Take

Upgrade Nextcloud Server to versions 19.0.13, 20.0.11, or 21.0.3 to address the vulnerability. Ensure no user account reuse or token persistence to safeguard against unauthorized access.

Long-Term Security Practices

Implement robust user authentication protocols, regular security audits, and user access reviews to maintain a secure Nextcloud Server environment.

Patching and Updates

Stay informed about security advisories and promptly apply patches and updates to mitigate emerging threats and bolster the security posture of Nextcloud Server.