Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
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 Data Obfuscation (T1001); ranked at the 44th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2023-43651
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…
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known token they also have access to. user_oidc 1.3.3 contains a patch. No known workarounds are available.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
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.
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.
Cryptography control addresses proper use of authentication algorithms but is broader than authentication alone.
A.8.25 mandates security requirements, secure coding, checkpoints, testing and developer capability in the SDLC which reaches incorrect algorithm implementation for auth (via secure coding, testing and vuln prevention/fixing), but this is only a minority slice of the weakness class as most instances arise from flawed design/requirements rather than implementation errors caught in dev.
Application security requirements can specify correct authentication algorithm use but do not guarantee correct implementation.
Secure coding practices reduce the likelihood of incorrect authentication algorithm implementation.
Security testing can detect flawed authentication implementations but does not prevent them by itself.