CVE-2026-45275: Nextcloud Approval App Privilege Escalation & Authorization Bypass

Technical summary

CVE-2026-45275 is a privilege escalation vulnerability stemming from improper authorization checks in the Nextcloud Approval app (CWE-285). The flaw permits an authenticated user to initiate file sharing with approvers despite lacking the necessary sharing permissions. The vulnerability exists because the approval workflow does not adequately validate whether the requesting user has authorization to share the targeted file, resulting in an authorization bypass that elevates the user's effective privileges. The attack vector is network-based and requires only valid user credentials; no additional interaction or special configuration is needed.

Business impact

This vulnerability creates a data governance and compliance risk. Employees or contractors without file-sharing authority can circumvent access controls to distribute sensitive documents to approval workflows, potentially exposing confidential, regulated, or proprietary information. Organizations relying on Nextcloud's permission model for data classification and handling may experience unauthorized disclosure of restricted materials. In regulated environments (healthcare, finance, legal), such breaches could trigger audit findings and compliance violations.

Affected systems

Nextcloud Approval app versions prior to 2.7.2 are affected. Both on-premises and cloud-hosted deployments using the vulnerable app version are at risk. Verify your installed version against the vendor advisory to confirm exposure.

Exploitability

The vulnerability has a CVSS score of 6.5 (Medium). Exploitation requires valid user credentials and network access; no special privileges, complex attack chains, or user interaction are needed. Any authenticated user in the Nextcloud instance can trigger the flaw, making it relatively straightforward to exploit once an account is obtained. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog as of the publication date.

Remediation

Upgrade Nextcloud to version 2.7.2 or later. Review file-sharing policies and audit logs to identify whether unauthorized sharing has occurred via the Approval app in your deployment. Consider restricting the Approval app to trusted administrators pending patch deployment if immediate upgrade is not feasible.

Patch guidance

Apply Nextcloud version 2.7.2 or later as provided by the vendor. Test the update in a non-production environment first to ensure compatibility with customizations or dependent apps. After patching, validate that existing approval workflows function correctly and that the authorization checks are now enforced.

Detection guidance

Monitor Nextcloud audit logs for unusual file-sharing activity initiated via the Approval app, particularly shares created by users who do not normally have sharing permissions. Look for access patterns where the requesting user and the sharing action do not align with documented roles. Network monitoring can detect outbound traffic patterns if shared files are subsequently accessed by unintended recipients.

Why prioritize this

Although scored as Medium severity, this vulnerability warrants prompt attention because it directly undermines your access control model and can lead to undetected data leaks. The low barrier to exploitation (any user account) and the compliance implications in regulated sectors elevate practical risk. Organizations managing sensitive or classified information should prioritize patching within 1–2 weeks.

Risk score, explained

The CVSS 3.1 score of 6.5 reflects a network-accessible vulnerability requiring authentication and resulting in high confidentiality impact (unauthorized file access) with no integrity or availability impact. The 'Low' complexity and lack of user interaction lower the score from a higher severity band, but the authorization bypass nature and ease of exploitation argue for faster remediation than the score alone might suggest.

Frequently asked questions