CVE-2026-45156
Published: 01 June 2026
Summary
CVE-2026-45156 is a high-severity Improper Authentication (CWE-287) vulnerability. Its CVSS base score is 8.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Valid Accounts (T1078); ranked at the 24.7th 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-2026-33675
Vulnerability details
Nextcloud is an open source content collaboration platform. From versions 0.3.0 to before 3.1.0, 5.0.0 to before 5.1.0, and 6.0.0 to before 6.4.0, a missing signature verification in User OIDC allowed a malicious ID4me authority to identify as any user.…
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This issue has been patched in versions 3.1.0, 4.1.0, 5.1.0, 6.4.0 and 8.3.0.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Missing OIDC signature verification enables impersonation via valid accounts (T1078) on a public-facing collaboration platform (T1190).
CVEs Like This One
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Detects unauthorized successful logons resulting from improper authentication implementations.
Documented procedures ensure personnel are trained on authentication mechanisms, tangibly lowering the risk of improper authentication being exploited.
Security awareness training instructs users on secure authentication practices and avoiding credential compromise.
Training on authentication mechanisms and best practices decreases the occurrence of improper authentication.
Non-repudiation requires strong authentication mechanisms to irrefutably attribute performed actions to specific individuals or processes.
Session content review can reveal authentication bypasses or failures in session establishment.
Review of authentication-related audit records can detect improper authentication mechanisms or bypasses.
Assessments check authentication mechanisms for correct implementation and effectiveness, reducing successful authentication bypass attempts.