What’s Vulnerable › Vulnerabilities

CVE-2023-39953: Issuer not verified from obtained token in user_oidc

• Severity: medium (CVSS 4.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-08-10 · updated 2026-06-17
• Weakness: CWE-303

Description

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

How to fix

Upgrade to a fixed version: nextcloud User Oidc 1.3.3. Check the vendor advisory for mitigations.

References

• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xx3h-v363-q36j
• https://github.com/nextcloud/user_oidc/pull/642
• https://hackerone.com/reports/2021684
• https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xx3h-v363-q36j
• https://github.com/nextcloud/user_oidc/pull/642
• https://hackerone.com/reports/2021684

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