CVE-2026-40896: OpenProject Auth Bypass Vulnerability

CVE-2026-40896 Overview

OpenProject, an open-source web-based project management platform, contains a critical Insecure Direct Object Reference (IDOR) vulnerability in its meeting agenda functionality. Prior to version 17.3.0, a user with manage_agendas permission in any project can inject agenda items into meetings belonging to any other project on the instance — even projects they have no access to. This authorization bypass allows attackers to blindly spray items into every meeting across the entire OpenProject instance by iterating sequential section IDs, requiring no knowledge of the target project, meeting, or victim.

Critical Impact

Attackers with minimal privileges can inject arbitrary content into meetings across the entire OpenProject instance, potentially disrupting operations, injecting malicious content, or manipulating project communications without any access to the target projects.

Affected Products

• OpenProject versions prior to 17.3.0
• All OpenProject instances with multi-project configurations
• Environments where users have manage_agendas permission in at least one project

Discovery Timeline

• 2026-04-20 - CVE CVE-2026-40896 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-40896

Vulnerability Analysis

This vulnerability stems from a Time-of-Check Time-of-Use (TOCTOU) race condition weakness (CWE-367) combined with missing authorization checks in the meeting agenda functionality. The application fails to properly validate that a user has appropriate permissions to modify agenda items in a specific meeting before allowing the modification to proceed. While the system correctly validates that the user has manage_agendas permission, it does not verify that this permission extends to the specific project or meeting being targeted.

The attack can be executed over the network without user interaction, requiring only low-level privileges (the manage_agendas permission in any single project). The vulnerability primarily impacts data integrity, as attackers can inject unauthorized content into meetings they should not have access to.

Root Cause

The root cause of this vulnerability lies in the improper authorization model within OpenProject's meeting agenda subsystem. The application uses sequential section IDs for meeting agenda items, making them easily predictable and enumerable. When processing requests to add or modify agenda items, the backend validates only that the requesting user possesses the manage_agendas permission globally but fails to enforce project-level access controls. This architectural flaw allows cross-project data manipulation without proper authorization boundaries.

Attack Vector

The attack vector is network-based and can be exploited by any authenticated user with manage_agendas permission in at least one project. An attacker can enumerate sequential section IDs to blindly target meetings across all projects on the instance. The attack requires no knowledge of the target project structure, meeting details, or victim identities. By systematically iterating through section ID values, an attacker can inject agenda items into meetings belonging to projects they have no legitimate access to, potentially affecting the entire organization's meeting infrastructure.

The exploitation technique involves sending crafted HTTP requests to the agenda item creation endpoint with section IDs belonging to meetings in other projects. Since section IDs are sequential and predictable, an attacker can easily script this attack to spray malicious content across hundreds or thousands of meetings.

Detection Methods for CVE-2026-40896

Indicators of Compromise

• Unusual spikes in agenda item creation requests from single user accounts
• Agenda items appearing in meetings from users who are not members of the associated project
• Sequential section ID access patterns indicating enumeration activity
• HTTP request logs showing agenda manipulation targeting multiple unrelated projects

Detection Strategies

• Monitor application logs for cross-project agenda item insertions where the requesting user lacks project membership
• Implement rate limiting and anomaly detection on agenda item creation endpoints
• Review audit logs for users creating agenda items in projects they do not have explicit access to
• Deploy web application firewall rules to detect sequential ID enumeration patterns

Monitoring Recommendations

• Enable detailed audit logging for all meeting and agenda-related operations in OpenProject
• Configure alerts for agenda modifications by users without project membership
• Monitor for unusual patterns in API requests to meeting-related endpoints
• Implement SentinelOne's application monitoring to detect anomalous behavior patterns in web application traffic

How to Mitigate CVE-2026-40896

Immediate Actions Required

• Upgrade OpenProject to version 17.3.0 or later immediately
• Review meeting audit logs for any unauthorized agenda item injections
• Audit user permissions to identify accounts with manage_agendas capability
• Temporarily restrict manage_agendas permission to trusted administrators if immediate patching is not possible

Patch Information

OpenProject has released version 17.3.0 which addresses this vulnerability. The fix implements proper project-level authorization checks to ensure users can only modify agenda items in meetings belonging to projects they have explicit access to. The security patch is available through the GitHub commit and details are documented in the GitHub Security Advisory GHSA-hh5p-gwf8-h245.

Organizations should prioritize this update, particularly those with multi-tenant or multi-project OpenProject deployments where cross-project access control is critical.

Workarounds

• Restrict manage_agendas permission to only highly trusted users until the patch can be applied
• Implement network-level access controls to limit access to OpenProject administrative functions
• Deploy a web application firewall to detect and block sequential ID enumeration attempts
• Enable comprehensive logging and monitoring on all meeting-related API endpoints

# Configuration example for reviewing user permissions in OpenProject
# List all users with manage_agendas permission for review
openproject run rails runner "Role.joins(:role_permissions).where(role_permissions: {permission: 'manage_agendas'}).each { |r| puts \"Role: #{r.name}\" }"

# Review recent agenda item modifications across all projects
openproject run rails runner "MeetingAgendaItem.where('created_at > ?', 7.days.ago).includes(:author, :meeting).each { |item| puts \"#{item.author&.name} created item in #{item.meeting&.project&.name}\" }"