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CVE-2026-45156— Nextcloud: Authentication Bypass in ID4me handling via Missing JWT Signature Verification in User OIDC

Quick assessment

Affected
nextcloud security-advisories
Exploitation
Public or AI PoC available; prioritize validation
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Nextcloud user_oidc是德国Nextcloud公司的一个应用程序 Nextcloud user_oidc 0.3.0版本至3.1.0之前版本、5.0.0版本至5.1.0之前版本和6.0.0版本至6.4.0之前版本存在授权问题漏洞，该漏洞源于User OIDC签名验证缺失，可能导致恶意ID4me权威机构冒充任何用户。

CVSS 8.1 · High EPSS 0.55% · P44

Possible ATT&CK Techniques 1 AI

T1078 · Valid Accounts

Affected Version Matrix 3

VendorProduct Version RangeStatus
nextcloud security-advisories >= 0.3.0, < 3.1.0 affected
>= 5.0.0, < 5.1.0 affected
>= 6.0.0, < 6.4.0 affected
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I. Basic Information for CVE-2026-45156

Vulnerability Information
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Vulnerability Title
Nextcloud: Authentication Bypass in ID4me handling via Missing JWT Signature Verification in User OIDC
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
Source: CVE Program / CVE List V5
Vulnerability Type
认证机制不恰当
Source: CVE Program / CVE List V5
Vulnerability Title
Nextcloud user_oidc 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Nextcloud user_oidc是德国Nextcloud公司的一个应用程序 Nextcloud user_oidc 0.3.0版本至3.1.0之前版本、5.0.0版本至5.1.0之前版本和6.0.0版本至6.4.0之前版本存在授权问题漏洞，该漏洞源于User OIDC签名验证缺失，可能导致恶意ID4me权威机构冒充任何用户。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
nextcloud security-advisories >= 0.3.0, < 3.1.0 -

II. Public POCs for CVE-2026-45156

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III. Intelligence Information for CVE-2026-45156

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Patches & Fixes for CVE-2026-45156 (1)

Vendor Advisories for CVE-2026-45156 (1)

Same Patch Batch · nextcloud · 2026-06-01 · 26 CVEs total

CVE-2026-45545 8.2 HIGH Nextcloud: SQL Injection in Column Type Parameter Allows Arbitrary SQL Execution
CVE-2026-45281 8.1 HIGH Nextcloud: Cross-Account Calendar Takeover via Unauthorized Group-Member-Set Update
CVE-2026-45722 7.1 HIGH Nextcloud: Tables app allows limited SQLi in ORDER BY with malicious sort order argument f
CVE-2026-45810 6.8 MEDIUM Nextcloud: Propfind requests for file comments allowed to load comments for other files
CVE-2026-45275 6.5 MEDIUM Nextcloud: Authorization bypass in approval feature allows unauthorized file sharing with
CVE-2026-45267 6.5 MEDIUM Nextcloud: Missing permission check for from submissions
CVE-2026-45282 6.5 MEDIUM Nextcloud: Logged-in user bypasses share password and download restrictions on Text attach
CVE-2026-45285 6.4 MEDIUM Nextcloud: Hidden Public Link creation when sharing to a Team External Member
CVE-2026-45157 6.3 MEDIUM Nextcloud: Valid share tokens allow to access tempory upload files of share owner
CVE-2026-45283 6.3 MEDIUM Nextcloud: Files Lock app allows users to lock and unlock files of other users
CVE-2026-45690 5.9 MEDIUM Nextcloud: Two-Factor Authentication Bypass via Pending Session Token Replay
CVE-2026-45691 5.9 MEDIUM Nextcloud: Bypass of second factor authentication on DAV endpoints
CVE-2026-45543 5.3 MEDIUM Nextcloud: Deleting a Forms collaborator share leaves uploaded response files accessible t
CVE-2026-45284 4.6 MEDIUM Nextcloud: Wrong condition in the User OIDC app's LdapService allowed deleted LDAP users t
CVE-2026-45153 4.6 MEDIUM Nextcloud: PIN bypass in PassCodeActivity via back button
CVE-2026-45279 4.4 MEDIUM Nextcloud: Limited path traversal via template API if using `{lang}` in config
CVE-2026-45286 4.3 MEDIUM Nextcloud: Calendar app leaked user identifiers via attendee suggestion endpoint
CVE-2026-45544 4.3 MEDIUM Nextcloud: Information Disclosure of view filter metdata via Broken Sensitive Data Masking
CVE-2026-45264 4.3 MEDIUM Nextcloud: ACL Rename Permission Bypass in Team Folders Allows Unauthorized File Renames
CVE-2026-45159 3.5 LOW Nextcloud: Files drop share links for end-to-end encrypted folders allowed to drop files i

Showing top 20 of 26 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: security-advisories
Same vendor: nextcloud
Same weakness: CWE-287

V. Comments for CVE-2026-45156

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