Vulnerability Report

CVE-2025-66558

Title: Nextcloud Twofactor WebAuthn Missing Ownership Check

Auth Bypass

Proof Of Concept

No public PoC currently indexed for CVE-2025-66558.

CWE Category CWE-639
Published Date Dec 05, 2025
Modified Date Oct 15, 2026
Exploit Status Not Found
Score 3.1 CVSS v3.1
Exploit Probability (EPSS)
0.28%

Vulnerability Summary

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.

Impacted Vendors

N
nextcloud 1

Reference Links

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
CVSS v3.1
Source Entity [email protected]
Severity LOW
3.1
Attack Vector
NETWORK
Complexity
HIGH
Privileges
N/A
Interaction
NONE
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N
CVSS v3.1
Source Entity [email protected]
Severity MEDIUM
4.3
Attack Vector
NETWORK
Complexity
LOW
Privileges
N/A
Interaction
REQUIRED
Confidentiality
N/A
Integrity
N/A
Availability
N/A
Scope
UNCHANGED
RAW VECTOR CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns

CVE-2025-66558 Exploits & PoCs (Proof Of Concept)

No public PoCs found in our database for this CVE.

MODIFIED

Vulnerability data updated via NVD.

MODIFIED

Vulnerability data or affected products updated.

MODIFIED

Vulnerability data updated via NVD.

PUBLISHED

Vulnerability first announced in NVD.

Attack Vector Matrix

Access Vector NETWORK
Complexity HIGH
Privileges N/A
Interaction NONE
CVSS Vector String CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:N

Affected Stack

No specific products linked.