CVE-2026-45275 Overview
CVE-2026-45275 is a privilege escalation vulnerability in the Nextcloud Approval app, an open source content collaboration platform extension. The flaw allows an authenticated user without sharing permissions to force the system to share a file with approvers. This results in an authorization bypass [CWE-285] and unauthorized distribution of restricted files. The issue affects Nextcloud Approval versions prior to 2.7.2 and is fixed in version 2.7.2.
Critical Impact
Authenticated users without share permissions can bypass authorization controls and distribute restricted files to approvers, breaching file confidentiality boundaries.
Affected Products
- Nextcloud Approval app versions prior to 2.7.2
- Nextcloud server instances with the Approval app enabled
- Deployments relying on Approval workflow for restricted document handling
Discovery Timeline
- 2026-06-01 - CVE-2026-45275 published to NVD
- 2026-06-03 - Last updated in NVD database
Technical Details for CVE-2026-45275
Vulnerability Analysis
The Nextcloud Approval app implements a workflow where designated approvers review files submitted by users. The vulnerability stems from the app trusting client-supplied requests to share submitted files with approvers, without first validating whether the requesting user holds the required sharing permission on the file.
An authenticated user can submit a file into the approval workflow even when they lack the standard share rights. The app then performs the share operation under elevated context, effectively distributing the file to approvers. The result is an authorization bypass mapped to [CWE-285], enabling horizontal privilege escalation against the sharing subsystem.
The vulnerability requires network access and low privileges, with no user interaction. Impact is limited to confidentiality, as integrity and availability of stored data remain intact.
Root Cause
The Approval app does not enforce a server-side check that the submitting user holds sharing permission on the target file before invoking the share action toward approvers. The missing authorization check is the focus of the upstream patch in Nextcloud Approval Pull Request #392.
Attack Vector
An authenticated user with access to a file but without sharing rights triggers the approval workflow on that file. The Approval app then shares the file with one or more configured approvers, leaking content that the requester was never authorized to redistribute. Exploitation requires only standard application access over the network.
No verified public proof-of-concept code is available. Refer to the Nextcloud Security Advisory GHSA-v8q8-w6c3-3gv9 and HackerOne Report #3593780 for additional technical context.
Detection Methods for CVE-2026-45275
Indicators of Compromise
- Approval app share events where the initiating user does not hold prior share permissions on the file.
- Files appearing in approver inboxes that were not previously shared through standard sharing flows.
- Audit log entries showing approval submissions from users lacking the share privilege on referenced files.
Detection Strategies
- Correlate Nextcloud audit logs to identify share events originating from the Approval app where the requester's effective permissions on the file exclude share.
- Review installed Approval app versions across Nextcloud instances and flag any below 2.7.2.
- Inspect the Approval workflow configuration to identify approver groups that may have received files outside expected sharing policies.
Monitoring Recommendations
- Centralize Nextcloud application and audit logs in a SIEM and alert on Approval-driven share events tied to users without prior share rights.
- Track installation of Nextcloud apps and their versions to detect outdated Approval app deployments.
- Monitor approver mailboxes and group activity for unexpected file distributions following CVE disclosure.
How to Mitigate CVE-2026-45275
Immediate Actions Required
- Upgrade the Nextcloud Approval app to version 2.7.2 or later on all Nextcloud instances.
- Inventory Approval workflows and identify files that may have been improperly shared since deployment.
- Restrict the Approval app to trusted user groups until patching is complete.
Patch Information
Nextcloud released version 2.7.2 of the Approval app, which adds the missing authorization check before sharing files with approvers. The fix is published in the Nextcloud Approval Pull Request #392 and described in the GitHub Security Advisory GHSA-v8q8-w6c3-3gv9.
Workarounds
- Disable the Approval app on affected Nextcloud instances until version 2.7.2 can be installed.
- Limit user accounts permitted to invoke approval workflows to trusted users only.
- Apply stricter file access policies that constrain which files can enter the Approval workflow.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
