CVE-2023-39953

Name: CVE-2023-39953
Creator: NVD / NIST
Published: 2023-08-10T14:15:15.37+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 4.8/10EPSS 0.45%

Last modified Jun 17, 2026

CVE-2023-39953 is a medium-severity vulnerability rated 4.8/10 on the CVSS scale. 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. EPSS estimates a 0.45% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

4.8/10

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N

EPSS Probability

0.45%

35.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-303

Affected Software

Vendor	Product	Versions
Nextcloud	User Oidc	>= 1.0.0, < 1.3.3

References

https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xx3h-v363-q36jPatch, Vendor Advisory
https://github.com/nextcloud/user_oidc/pull/642Patch
https://hackerone.com/reports/2021684Permissions Required
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-xx3h-v363-q36jPatch, Vendor Advisory
https://github.com/nextcloud/user_oidc/pull/642Patch
https://hackerone.com/reports/2021684Permissions Required

Timeline

Published: Aug 10, 2023
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2023-39953?

How severe is CVE-2023-39953?

CVE-2023-39953 has a CVSS score of 4.8/10 (MEDIUM severity). The EPSS model estimates a 0.45% probability of exploitation in the next 30 days.

How do I fix CVE-2023-39953?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2023-39953?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST