CVE-2023-39953: Nextcloud User Oidc

Medium severity, CVSS 4.8. EPSS: 0.5% chance of exploitation in the next 30 days.

user_oidc provides the OIDC connect user backend for Nextcloud, an open-source cloud platform. Starting in version 1.0.0 and prior to version 1.3.3, missing verification of the issuer would have allowed an attacker to perform a man-in-the-middle attack returning corrupted or known token they also have access to. user_oidc 1.3.3 contains a patch. No known workarounds are available.

Affected products

• Nextcloud User Oidc: from 1.0.0, before 1.3.3 (fixed in 1.3.3)

Published 2023-08-10. Last modified 2026-06-17.