What’s Vulnerable › Vulnerabilities

CVE-2025-66558: Nextcloud Twofactor WebAuthn app was updated based on public key

• Severity: medium (CVSS 4.3 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-12-05 · updated 2026-10-15
• Weakness: CWE-639

Description

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; from 2.0.0 before 2.4.1 — fixed in 1.4.2, 2.4.1

How to fix

Upgrade to a fixed version: nextcloud Two-Factor Webauthn 1.4.2, 2.4.1. Check the vendor advisory for mitigations.

References

• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-fr8x-mvjg-wf9q
• https://github.com/nextcloud/twofactor_webauthn/commit/5d2302166d31ee2e01b2e21556bd5372156da13d
• https://github.com/nextcloud/twofactor_webauthn/pull/881
• https://hackerone.com/reports/3360354

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