High severity · published Jun 1, 2026
CVE-2026-45156
Nextcloud: Authentication Bypass in ID4me handling via Missing JWT Signature Verification in User OIDC
8.1
CVSS
0.4%
EPSS
No
On KEV
Description
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. This issue has been patched in versions 3.1.0, 4.1.0, 5.1.0, 6.4.0 and 8.3.0.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
Required
Confidentiality
High
Integrity
High
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 35% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
SE
security-advisories · nextcloud
>= 0.3.0, < 3.1.0; >= 5.0.0, < 5.1.0; >= 6.0.0, < 6.4.0 · source: vendor
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-45156
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-45156
github.com
https://github.com/nextcloud/security-advisories/security/advisories/GHSA-qqgv-fqwp-mjpp
github.com
https://github.com/nextcloud/user_oidc/pull/1285
hackerone.com
https://hackerone.com/reports/3489490
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