CVE-2026-45156 Nextcloud: Authentication Bypass in ID4me handling via Missing JWT Signature Verification in User OIDC
Attackers can bypass authentication and impersonate any user due to missing JWT signature verification in Nextcloud's ID4me OIDC handling.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- None listed
What is CVE-2026-45156?
CVE-2026-45156 is a high-severity authentication bypass vulnerability in nextcloud security-advisories, published on 1 Jun 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official 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.
Weakness: CWE-287
Which versions are affected by CVE-2026-45156?
How do I fix CVE-2026-45156?
No fix has been published for CVE-2026-45156 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-45156 being exploited?
There is no known exploitation of CVE-2026-45156 in the wild and no public exploit code.
Public exploit code: 1 proofs of concept on GitHub.
Sources
Also known as GHSA-qqgv-fqwp-mjpp.