Missing Signature Verification in Nextcloud OIDC Enables User Impersonation
CVE-2026-45156

8.1HIGH

Key Information:

Vendor

Nextcloud
Status
Security-advisories
Vendor
CVE Published:
1 June 2026

Badges

👾 Exploit Exists🟡 Public PoC

What is CVE-2026-45156?

false

Affected Version(s)

security-advisories >= 0.3.0, < 3.1.0 < 0.3.0, 3.1.0

security-advisories >= 5.0.0, < 5.1.0 < 5.0.0, 5.1.0

security-advisories >= 6.0.0, < 6.4.0 < 6.0.0, 6.4.0

Exploit Proof of Concept (PoC)

PoC code is written by security researchers to demonstrate the vulnerability can be exploited. PoC code is also a key component for weaponization which could lead to ransomware.

CVE-2026-45156-POC
Created by cybertechajju

References

https://github.com/nextcloud/security-advisories/security...
x_refsource_CONFIRM
https://github.com/nextcloud/user_oidc/pull/1285
x_refsource_MISC
https://hackerone.com/reports/3489490
x_refsource_MISC

CVSS V3.1

Score:
8.1
Severity:
HIGH
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Unchanged

Timeline

  • 🟡

    Public PoC available

  • 👾

    Exploit known to exist

  • Vulnerability published

  • Vulnerability Reserved

.