CVE-2025-66558: Nextcloud Two-Factor Webauthn

Medium severity, CVSS 4.3. EPSS: 0.3% chance of exploitation in the next 30 days.

Nextcloud Twofactor WebAuthn is the WebAuthn Two-Factor Provider for Nextcloud. Prior to 1.4.2 and 2.4.1, a missing ownership check allowed an attack to take-away a 2FA webauthn device when correctly guessing a 80-128 character long random string of letters, numbers and symbols. The victim would then be prompted to register a new device on the next login. The attacker can not authenticate as the victim. This vulnerability is fixed in 1.4.2 and 2.4.1.

Affected products

• Nextcloud Two-Factor Webauthn: from 1.0.0, before 1.4.2 (fixed in 1.4.2); from 2.0.0, before 2.4.1 (fixed in 2.4.1)

Published 2025-12-05. Last modified 2026-06-17.