Cyber Resilience

CVE-2023-39953

Auth Bypass in Nextcloud User Oidc 1.0.0 – 1.3.3

Auth Bypass
Published
10 August 2023
Modified
21 November 2024
Patch / advisory
View advisory
CVSS Score v3.1 4.8
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N
EPSS Score 0.0054 43th percentile
Risk Priority 40 floored blend · peak EPSS

Summary

CVE-2023-39953 is a medium-severity Incorrect Implementation of Authentication Algorithm (CWE-303) vulnerability in Nextcloud User Oidc. Its CVSS base score is 4.8 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique External Remote Services (T1133); ranked at the 43th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

OWASP Top 10 for Web (2025)

A07:2025 Authentication Failures

EU & UK References

Vulnerability Data

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…

more

known token they also have access to. user_oidc 1.3.3 contains a patch. No known workarounds are available.

CWE(s)
CWE-303

Related Threats

MITRE ATT&CK Enterprise Techniques

T1133 External Remote Services Persistence
Adversaries may leverage external-facing remote services to initially access and/or persist within a network.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2023-28848Same product: Nextcloud User Oidc
CVE-2024-37312Same product: Nextcloud User Oidc
CVE-2026-45284Same product: Nextcloud User Oidc
CVE-2026-45278Same product: Nextcloud User Oidc
CVE-2023-32074Same product: Nextcloud User Oidc
CVE-2023-39954Same product: Nextcloud User Oidc
CVE-2024-37886Same product: Nextcloud User Oidc
CVE-2024-52512Same product: Nextcloud User Oidc
CVE-2024-22212Same vendor: Nextcloud
CVE-2025-47791Same vendor: Nextcloud

Affected Assets

nextcloud
user oidc
1.0.0 — 1.3.3

Mitigating Controls

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require correct implementation of authentication algorithms.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.5 Secure authentication full match
degrades

Secure authentication control directly requires correct implementation of authentication algorithms.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect flawed authentication implementations but does not prevent them by itself.

A.8.24 Use of cryptography partial match
degrades

Cryptography control addresses proper use of authentication algorithms but is broader than authentication alone.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle includes verification steps that can catch incorrect authentication implementations.

A.8.26 Application security requirements partial match
prevents

Application security requirements can specify correct authentication algorithm use but do not guarantee correct implementation.

A.8.28 Secure coding partial match
prevents

Secure coding practices reduce the likelihood of incorrect authentication algorithm implementation.

References