CVE-2026-6572: Collabora KodExplorer Auth Bypass Flaw

CVE-2026-6572 Overview

A security vulnerability has been detected in Collabora KodExplorer up to version 4.52. This issue affects the file /app/controller/share.class.php within the fileUpload Endpoint component. The manipulation of the fileUpload argument leads to improper authorization (CWE-266), potentially allowing unauthorized users to upload files through the affected endpoint. Remote exploitation is possible, though the attack complexity is rated as high and exploitation is known to be difficult. The exploit has been disclosed publicly and may be used. The vendor was contacted early about this disclosure but did not respond in any way.

Critical Impact

Improper authorization in the fileUpload endpoint could allow unauthenticated attackers to upload arbitrary files remotely, potentially leading to unauthorized data modification, malicious file placement, or further system compromise.

Affected Products

• Collabora KodExplorer up to version 4.52
• KodExplorer fileUpload Endpoint (/app/controller/share.class.php)

Discovery Timeline

• 2026-04-19 - CVE CVE-2026-6572 published to NVD
• 2026-04-22 - Last updated in NVD database

Technical Details for CVE-2026-6572

Vulnerability Analysis

This vulnerability stems from improper authorization handling in the KodExplorer file sharing component. The fileUpload endpoint within /app/controller/share.class.php fails to properly validate user permissions before processing file upload requests. This authorization bypass allows remote attackers to potentially upload files without proper authentication or authorization checks being enforced.

The vulnerability is classified under CWE-266 (Incorrect Privilege Assignment), indicating that the application incorrectly grants elevated privileges or access rights during the file upload process. While the attack requires network access and involves high complexity, successful exploitation could compromise the integrity of the file storage system.

Root Cause

The root cause of this vulnerability lies in insufficient authorization checks within the share.class.php file's fileUpload handling logic. The affected code fails to verify that the requesting user has appropriate permissions before allowing file upload operations. This creates a privilege escalation path where users can bypass intended access controls by directly manipulating the fileUpload parameter.

Attack Vector

The attack vector is network-based, allowing remote exploitation without requiring local access to the target system. An attacker can craft malicious HTTP requests targeting the /app/controller/share.class.php endpoint, manipulating the fileUpload argument to bypass authorization controls. The attack does not require user interaction, but the high complexity rating suggests that specific conditions must be met or significant technical knowledge is required for successful exploitation.

The vulnerability involves manipulating file upload parameters sent to the share.class.php controller. When the fileUpload endpoint receives a crafted request, it fails to properly validate the requester's authorization level, potentially allowing unauthorized file operations. For detailed technical analysis, refer to the VulDB Vulnerability Detail or the VulnPlus security note.

Detection Methods for CVE-2026-6572

Indicators of Compromise

• Unexpected HTTP POST requests to /app/controller/share.class.php with fileUpload parameters from unknown or unauthenticated sources
• Unusual file creation activity in KodExplorer shared directories without corresponding authenticated user sessions
• Web server logs showing repeated access attempts to the fileUpload endpoint with varying payloads
• Presence of suspicious or unexpected files in upload directories that do not match legitimate user activity

Detection Strategies

• Implement web application firewall (WAF) rules to monitor and filter requests to /app/controller/share.class.php containing suspicious fileUpload parameters
• Enable verbose logging for the KodExplorer application to capture all file upload attempts and associated authentication context
• Deploy file integrity monitoring on KodExplorer upload directories to detect unauthorized file additions

Monitoring Recommendations

• Monitor HTTP access logs for unusual patterns of requests targeting the share controller endpoint
• Set up alerts for file upload activities that occur outside of normal business hours or from unexpected IP ranges
• Review uploaded file types and sizes for anomalies that may indicate exploitation attempts

How to Mitigate CVE-2026-6572

Immediate Actions Required

• Restrict network access to KodExplorer instances using firewall rules or network segmentation until a patch is available
• Implement additional authentication layers or access controls in front of the vulnerable endpoint
• Review and audit all recently uploaded files for potential malicious content
• Consider disabling the file upload functionality temporarily if it is not critical to operations

Patch Information

No official patch information is currently available. The vendor was contacted early about this disclosure but did not respond. Organizations should monitor the VulDB entry and official KodExplorer channels for future security updates. Until a patch is released, implementing the workarounds below is strongly recommended.

Workarounds

• Implement IP-based access restrictions to limit who can reach the KodExplorer fileUpload endpoint
• Deploy a reverse proxy with additional authentication requirements before the vulnerable endpoint
• Disable or remove the share.class.php file if sharing functionality is not required in your deployment
• Monitor file system changes in real-time using host-based intrusion detection systems (HIDS)

# Example: Restrict access to the vulnerable endpoint using Apache .htaccess
# Place this in your KodExplorer directory

<Files "share.class.php">
    Order Deny,Allow
    Deny from all
    # Allow only trusted IP ranges
    Allow from 192.168.1.0/24
    Allow from 10.0.0.0/8
</Files>