Auth bypass in Nextcloud Security-Advisories
CVE-2025-66558
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.
Vulnerability class: IDOR (Insecure Direct Object Reference)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.1 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (18.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 18.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000
Affected products
- Nextcloud Security-Advisories — versions < 1.4.2, >= 2.0.0-beta.1, < 2.4.1
- Nextcloud Two-Factor Webauthn
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-fr8x-mvjg-wf9q (Patch, Vendor Advisory)
- github.com/nextcloud/twofactor_webauthn/pull/881 (Patch, Issue Tracking)
- github.com/nextcloud/twofactor_webauthn/commit/5d2302166d31ee2e01b2e21556bd5372… (Patch)
- hackerone.com/reports/3360354 (Permissions Required, Vendor Advisory)
Frequently asked questions
- What is CVE-2025-66558?
- CVE-2025-66558 is a low-severity vulnerability in Nextcloud Security-Advisories, classified under Authorization Bypass Through User-Controlled Key. CVSS score: 3.1/10. Published 2025-12-05.
- How severe is CVE-2025-66558?
- Low severity. CVSS v3 base score is 3.1 out of 10.