CVE-2026-40305: DNN CMS Auth Bypass Vulnerability

CVE-2026-40305 Overview

DNN (formerly DotNetNuke) is an open-source web content management platform (CMS) in the Microsoft ecosystem. A vulnerability exists in the friends feature that allows an authenticated user to craft a malicious request that forces the acceptance of a friend request on behalf of another user. This is a classic Improper Authorization vulnerability (CWE-285) that bypasses the intended access controls for social features within the CMS platform.

Critical Impact

An attacker with a valid DNN account can force-accept friend requests on behalf of other users, potentially enabling social engineering attacks, unauthorized access to restricted content shared among friends, or manipulation of social connections within the platform.

Affected Products

• DNN (DotNetNuke) versions 6.0.0 through 10.2.1
• DNN Platform installations using the friends feature
• Any web applications built on vulnerable DNN versions

Discovery Timeline

• 2026-04-17 - CVE CVE-2026-40305 published to NVD
• 2026-04-20 - Last updated in NVD database

Technical Details for CVE-2026-40305

Vulnerability Analysis

This vulnerability falls under the category of Improper Authorization (CWE-285), where the application fails to properly verify that a user has the necessary permissions to perform an action on a specific resource. In this case, the friends feature endpoint does not adequately validate that the authenticated user making the request is the same user who should be accepting a friend request.

The vulnerability affects DNN installations from version 6.0.0 up to but not including version 10.2.2. While the attack requires authentication (reducing the potential attack surface), it enables horizontal privilege escalation by allowing one authenticated user to perform actions that should only be available to another specific user.

The network-based attack vector with low complexity indicates that exploitation is straightforward once an attacker understands the request structure. The impact is primarily on confidentiality, as manipulating friend relationships could expose content or information shared between "friends" within the platform.

Root Cause

The root cause of this vulnerability is insufficient authorization checks in the friends feature request handler. The application fails to properly validate that the user initiating the friend request acceptance is the intended recipient of the friend request. This represents a broken access control pattern where the system trusts client-provided data or session information without adequately verifying the relationship between the authenticated user and the target action.

Attack Vector

An authenticated attacker can exploit this vulnerability by crafting HTTP requests to the friends feature endpoint. By manipulating request parameters, the attacker can force the acceptance of a friend request on behalf of a different user. This could be leveraged for:

1. Social Engineering - Building false connections to gain trust
2. Information Access - Viewing content shared only with friends
3. Account Manipulation - Altering the social graph within the application

The attack requires network access to the DNN installation and valid user credentials. No user interaction from the victim is required for exploitation.

For technical details on the vulnerability mechanism, refer to the GitHub Security Advisory GHSA-fpj4-9qhx-5m6m.

Detection Methods for CVE-2026-40305

Indicators of Compromise

• Unexpected friend relationships appearing in user accounts without user initiation
• Unusual patterns of friend request acceptances in application logs
• Multiple friend acceptance events originating from a single IP or session targeting different users
• Complaints from users about unauthorized friend connections

Detection Strategies

• Monitor HTTP request logs for anomalous patterns in friends feature API calls
• Implement logging that captures the authenticated user versus the target user in friend acceptance requests
• Review access logs for requests where the session user ID differs from the friend request recipient ID
• Deploy web application firewall (WAF) rules to detect parameter manipulation in social feature requests

Monitoring Recommendations

• Enable detailed logging for all social feature interactions within DNN
• Set up alerts for bulk friend acceptance events that exceed normal usage patterns
• Monitor for authentication patterns followed by immediate friend feature manipulation
• Review user reports of unexpected friend connections as potential indicators of exploitation

How to Mitigate CVE-2026-40305

Immediate Actions Required

• Upgrade DNN installations to version 10.2.2 or later immediately
• Audit existing friend relationships for any unauthorized connections
• Review access logs for evidence of exploitation prior to patching
• Consider temporarily disabling the friends feature if immediate upgrade is not possible

Patch Information

DNN Software has released version 10.2.2 which addresses this vulnerability. The patch is available via the official GitHub release. Organizations should prioritize this upgrade for any internet-facing DNN installations.

The fix implements proper authorization checks to ensure that only the intended recipient of a friend request can accept that request, preventing the horizontal privilege escalation attack.

Workarounds

• Disable the friends feature entirely until patching is possible if the feature is not critical to operations
• Implement network-level access controls to restrict access to DNN administrative and social features
• Deploy WAF rules to monitor and potentially block suspicious requests to friends feature endpoints
• Consider implementing additional authentication requirements for social feature actions as a defense-in-depth measure

# Verify DNN version and plan upgrade
# Check current DNN version in web.config or admin panel
# Download patched version from GitHub releases
# Test upgrade in staging environment before production deployment