CVE-2026-45156Network attack vector

User impersonation via unsigned ID4me login tokens

Published Jun 1, 2026 · Updated Jun 1, 2026

Authentication bypass in affected Nextcloud User OIDC releases allows remote attackers to impersonate any user through an ID4me login. Id4meController decodes the authority's JWT payload and creates or retrieves the named account without first verifying the token's cryptographic signature. ID4me must be enabled; affected ranges are 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, and exploitation requires interaction with a malicious authority's login flow.

CVSS severity8.1
High
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in affected Nextcloud User OIDC releases allows remote attackers to impersonate any user through an ID4me login. Id4meController decodes the authority's JWT payload and creates or retrieves the named account without first verifying the token's cryptographic signature. ID4me must be enabled; affected ranges are 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, and exploitation requires interaction with a malicious authority's login flow.

The record

CVE
CVE-2026-45156
Published
Jun 1, 2026
Updated
Jun 1, 2026
Vendor
Nextcloud GmbH
Product
Security Advisories
Classifications
CWE-287
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 1, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.3.0, < 3.1.0
  2. Affected versionversion=>= 5.0.0, < 5.1.0
  3. Affected versionversion=>= 6.0.0, < 6.4.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Nextcloud GmbH · Security Advisoriesversion=>= 0.3.0, < 3.1.0; version=>= 5.0.0, < 5.1.0; version=>= 6.0.0, < 6.4.0

Published CVSS scores

8.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-287Improper Authentication

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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