CVE-2026-57311: Windu CMS File Upload RCE Vulnerability

CVE-2026-57311 Overview

CVE-2026-57311 is an unrestricted file upload vulnerability in Windu CMS. The application does not validate the types of files uploaded through its interface. An authenticated attacker can upload arbitrary files, including PHP scripts, to the server. Once the uploaded script is requested, the web server executes it, resulting in Remote Code Execution (RCE) in the context of the web application.

The issue has been confirmed in Windu CMS version 4.1. Vendor contact attempts were unsuccessful, so other versions may also be affected. The weakness is categorized as [CWE-434] Unrestricted Upload of File with Dangerous Type.

Critical Impact
Authenticated attackers can achieve Remote Code Execution by uploading PHP files through the CMS upload functionality, leading to full compromise of the underlying web application.

Affected Products

Windu CMS 4.1 (confirmed)
Other Windu CMS versions may be affected but are unconfirmed due to unsuccessful vendor contact

Discovery Timeline

2026-07-20 - CVE-2026-57311 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-57311

Vulnerability Analysis

Windu CMS exposes a file upload feature to authenticated users. The upload handler accepts files without validating the file type, MIME content, or extension. An attacker with valid credentials can submit a file with a .php extension containing arbitrary PHP code. The server stores the file within a web-accessible directory, and the PHP interpreter processes it on subsequent HTTP requests. This transforms a routine upload feature into an arbitrary code execution primitive.

Because the vulnerability requires authentication, exploitation depends on the attacker holding valid credentials or acquiring them through phishing, credential stuffing, or a separate weakness. Once code execution is achieved, the attacker inherits the privileges of the web server process. This typically allows reading application secrets, tampering with content, pivoting to backend databases, and establishing persistent access.

Root Cause

The root cause is missing server-side validation of uploaded content [CWE-434]. The handler does not enforce an allow-list of permitted extensions, does not verify MIME types against file signatures, and does not store uploads outside of executable paths. Any of these controls, applied consistently, would break the exploitation chain.

Attack Vector

Exploitation occurs over the network against the CMS administrative or content upload endpoints. The attacker authenticates, submits a crafted multipart HTTP request containing a PHP payload, and then requests the resulting URL to trigger execution. Refer to the CERT Polska advisory for technical context on the Windu CMS vulnerability set and the Windu project site for product information.

Detection Methods for CVE-2026-57311

Indicators of Compromise

Newly created files with .php, .phtml, .php5, or double extensions such as .jpg.php inside Windu CMS upload directories.
HTTP POST requests to CMS upload endpoints followed shortly by GET requests to previously unseen script paths.
Web server process (php-fpm, apache2, www-data) spawning shells, network utilities, or writing to system directories.
Outbound connections initiated by the web server to attacker-controlled infrastructure after an upload event.

Detection Strategies

Monitor upload directories with file integrity monitoring and alert on the creation of executable script files.
Inspect web access logs for authenticated POST requests to upload endpoints followed by GETs to uncommon .php paths.
Correlate authentication events with subsequent file writes to identify accounts abusing the upload feature.
Apply YARA or signature-based scans against upload directories to detect PHP webshells such as eval($_POST, system(, or base64_decode patterns.

Monitoring Recommendations

Enable verbose logging on the CMS upload endpoint including authenticated user, source IP, filename, and content type.
Forward web server, PHP-FPM, and OS process telemetry to a centralized analytics platform for cross-source correlation.
Baseline normal child processes of the web server and alert on deviations such as sh, bash, curl, or wget invocations.
Track anomalous outbound connections from web-tier hosts, which often indicate post-exploitation command-and-control activity.

How to Mitigate CVE-2026-57311

Immediate Actions Required

Restrict access to the Windu CMS administrative interface using network controls, VPN, or IP allow-listing until a fix is available.
Audit all existing accounts and revoke unused or overly privileged credentials that can access the upload feature.
Scan CMS upload directories for unexpected .php files and remove any unauthorized scripts.
Configure the web server to deny execution of scripts within upload directories by adjusting handler mappings.

Patch Information

No vendor patch is currently available. CERT Polska reported that vendor contact attempts were unsuccessful. Administrators should assume the vulnerability remains unpatched across all Windu CMS versions and prioritize compensating controls. Track updates through the CERT Polska advisory and the Windu project site.

Workarounds

Reconfigure the web server to prevent execution of PHP files in upload directories, for example by disabling PHP handlers under /uploads.
Deploy a web application firewall rule that blocks uploads containing PHP tags or executable extensions.
Move upload storage to a location outside of the document root and serve files through a controlled download handler.
If the upload feature is not required, disable it entirely until the vendor releases a fix.

bash

# Example Apache configuration to disable PHP execution in the uploads directory
<Directory "/var/www/windu/uploads">
    php_admin_flag engine off
    SetHandler none
    RemoveHandler .php .phtml .php5
    RemoveType .php .phtml .php5
    Options -ExecCGI
</Directory>