CVE-2026-45156: Nextcloud Security-Advisories

High severity, CVSS 8.1. EPSS: 0.6% chance of exploitation in the next 30 days.

Nextcloud is an open source content collaboration platform. From versions 0.3.0 to before 3.1.0, 5.0.0 to before 5.1.0, and 6.0.0 to before 6.4.0, a missing signature verification in User OIDC allowed a malicious ID4me authority to identify as any user. This issue has been patched in versions 3.1.0, 4.1.0, 5.1.0, 6.4.0 and 8.3.0.

Affected products

• Nextcloud Security-Advisories: from 0.3.0, before 3.1.0 (fixed in 3.1.0); from 5.0.0, before 5.1.0 (fixed in 5.1.0); from 6.0.0, before 6.4.0 (fixed in 6.4.0)

Published 2026-06-01. Last modified 2026-07-22.