Auth bypass in Nextcloud Server
CVE-2026-45691
Nextcloud is an open source content collaboration platform. In Nextcloud Server from versions 32.0.0 to before 32.0.9, and 33.0.0 to before 33.0.3, a pre-2FA session cookie (created after successful password authentication but before TOTP completion) could be reused as a Bearer token to authenticate against DAV endpoints, granting read/write access and bypassing mandatory two-factor authentication. It is recommended that the Nextcloud Server is upgraded to 33.0.3 or 32.0.9. It is recommended that the Nextcloud Enterprise Server is upgraded to 33.0.3, 32.0.9, 31.0.14.5, 30.0.17.9 or 29.0.16.16
Vulnerability class: Broken Authentication
Published · last modified .
CVSS v3 metric
CVSS v3 base score 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:N.
EPSS exploit prediction
EPSS: 0.004 (35.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 35th percentile — 35.2% 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: 0.004 · change: +0.001
Affected products
- Nextcloud Server
- Nextcloud Security-Advisories — versions >= 32.0.0, < 32.0.9, >= 33.0.0, < 33.0.3
Weakness classification (CWE)
References
- github.com/nextcloud/security-advisories/security/advisories/GHSA-mp6x-g55j-w9jw (Vendor Advisory)
- github.com/nextcloud/server/pull/59758 (Patch, Issue Tracking)
- hackerone.com/reports/3573399 (Permissions Required)
Frequently asked questions
- What is CVE-2026-45691?
- CVE-2026-45691 is a medium-severity vulnerability in Nextcloud Server, classified under Improper Authentication. CVSS score: 5.9/10. Published 2026-06-01.
- How severe is CVE-2026-45691?
- Medium severity. CVSS v3 base score is 5.9 out of 10.