CVE-2026-40548: SOPlanning File Upload RCE Vulnerability

CVE-2026-40548 Overview

CVE-2026-40548 is an unrestricted file upload vulnerability in SOPlanning, an open-source online planning tool. The application fails to validate the extensions of files uploaded through its backup functionality. An authenticated attacker can submit a crafted ZIP archive that contains a legitimate user.csv file alongside a malicious payload. The server extracts the archive without sanitizing its contents. The flaw is tracked under CWE-434 and affects SOPlanning version 1.55 and below.

Critical Impact

When chained with CVE-2026-40547 (Path Traversal), an attacker can drop a PHP script into a web-accessible directory and trigger remote code execution through the browser.

Affected Products

• SOPlanning version 1.55
• SOPlanning versions prior to 1.55
• SOPlanning backup module

Discovery Timeline

• 2026-06-01 - CVE-2026-40548 published to NVD
• 2026-06-01 - Last updated in NVD database

Technical Details for CVE-2026-40548

Vulnerability Analysis

The vulnerability resides in the SOPlanning backup restoration workflow. The application accepts ZIP archives uploaded by authenticated users who have access to the backup feature. During extraction, the server writes the archive contents to disk without inspecting the file extensions or MIME types of the embedded files. An attacker can place arbitrary file types, including server-side scripts, into the archive.

The vulnerability is categorized as Unrestricted Upload of File with Dangerous Type. The exploitation impact depends on where the extracted files land on the file system. By itself, the flaw allows attackers to plant files. Combined with the companion path traversal vulnerability CVE-2026-40547, the attacker controls the destination path of each extracted file.

This chain enables placement of a PHP script inside the public web root. Once written, the file is reachable through a standard HTTP request, and the web server interprets and executes its contents. Further details are available in the CERT Poland Advisory.

Root Cause

The backup import routine trusts archive contents implicitly. It does not enforce an allow-list of permitted extensions, does not validate file signatures, and does not normalize destination paths. Together with the absence of path traversal protections, these gaps permit arbitrary write primitives on the host running SOPlanning.

Attack Vector

Exploitation requires network access and an authenticated session with high privileges sufficient to reach the backup functionality. The attacker prepares a ZIP archive that bundles the expected user.csv file with a malicious payload such as a .php web shell. The attacker submits the archive through the backup upload endpoint. The server extracts the payload to an attacker-controlled location when paired with CVE-2026-40547. The attacker then requests the planted file through the browser to execute it under the web server's identity.

No verified public exploit code is available. The vulnerability mechanism is documented in the CERT Poland Advisory.

Detection Methods for CVE-2026-40548

Indicators of Compromise

• Unexpected .php, .phtml, or other script files within SOPlanning web directories that were not part of the original installation.
• Backup archive uploads from authenticated users followed by HTTP requests to newly created files.
• Web server access logs showing GET or POST requests to script files in directories normally containing only data exports.
• File modification timestamps in web-accessible paths that align with backup restore operations.

Detection Strategies

• Monitor the SOPlanning installation directory for the creation of executable file types after backup operations.
• Inspect the contents of uploaded ZIP archives at the proxy or web application firewall layer for non-CSV file extensions.
• Correlate authenticated administrative actions on the backup endpoint with subsequent process executions spawned by the PHP interpreter.

Monitoring Recommendations

• Enable file integrity monitoring on the SOPlanning web root and configuration directories.
• Log all access to the backup upload and restore endpoints, including the authenticated user, source IP, and archive filename.
• Alert on web server worker processes spawning shell, network, or scripting utilities, which can indicate web shell activity following exploitation.

How to Mitigate CVE-2026-40548

Immediate Actions Required

• Restrict access to the SOPlanning backup functionality to a minimal set of trusted administrative accounts.
• Place SOPlanning behind a reverse proxy or VPN to limit network exposure of authenticated endpoints.
• Audit the SOPlanning web root for unexpected script files and remove any that cannot be attributed to the application installer.
• Rotate credentials for all SOPlanning administrative accounts as a precaution.

Patch Information

No vendor patch reference is listed in the published advisory at this time. Administrators should monitor the SOPlanning project page for releases after version 1.55 and apply updates as soon as they are available.

Workarounds

• Disable the backup upload feature in environments where it is not actively used.
• Configure the web server to deny execution of PHP files within directories that should only contain user-supplied data.
• Apply strict file system permissions so the web service account cannot write to executable script locations.
• Use a web application firewall rule to block uploaded archives whose contents include script extensions such as .php, .phtml, or .phar.

# Example Apache configuration to prevent PHP execution in upload directories
<Directory "/var/www/soplanning/process">
    php_admin_flag engine off
    <FilesMatch "\.(php|phtml|phar)$">
        Require all denied
    </FilesMatch>
</Directory>