CVE-2026-40909: WWBN AVideo RCE Vulnerability

CVE-2026-40909 Overview

WWBN AVideo is an open source video platform that contains a critical path traversal vulnerability in its locale save functionality. In versions 29.0 and prior, the locale save endpoint (locale/save.php) constructs a file path by directly concatenating user-supplied input from $_POST['flag'] without any sanitization. This allows attackers to write arbitrary PHP files to any writable location on the filesystem, achieving Remote Code Execution.

Critical Impact

An admin attacker (or any user who can CSRF an admin, since no CSRF token is checked and cookies use SameSite=None) can traverse out of the locale/ directory and write arbitrary .php files to any writable location on the filesystem, achieving Remote Code Execution.

Affected Products

• WWBN AVideo versions 29.0 and prior
• All installations using the vulnerable locale/save.php endpoint
• Systems where the web server has write permissions to sensitive directories

Discovery Timeline

• 2026-04-21 - CVE CVE-2026-40909 published to NVD
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2026-40909

Vulnerability Analysis

This vulnerability stems from improper input validation in the locale save functionality of WWBN AVideo. The locale/save.php endpoint at line 30 directly concatenates the $_POST['flag'] parameter into the file path without any sanitization or validation. Subsequently, at line 40, the $_POST['code'] parameter is written verbatim to that constructed path via fwrite().

The absence of path validation allows an attacker to include directory traversal sequences (such as ../) in the flag parameter, effectively escaping the intended locale/ directory. This enables writing malicious PHP files to arbitrary locations on the filesystem where the web server has write permissions.

Compounding the issue, the endpoint lacks CSRF token verification, and cookies are configured with SameSite=None. This means that even if direct admin access is unavailable, an attacker could potentially leverage a CSRF attack against an authenticated administrator to trigger the vulnerability.

Root Cause

The root cause is a classic CWE-22 (Path Traversal) vulnerability where user-controlled input is used to construct file paths without proper sanitization. The $_POST['flag'] parameter is directly concatenated into the file path, allowing directory traversal attacks. Additionally, the missing CSRF protection enables cross-origin exploitation scenarios.

Attack Vector

The attack requires network access and can be executed by an authenticated administrator directly or through CSRF exploitation of an administrator session. An attacker crafts a malicious POST request to locale/save.php with a specially crafted flag parameter containing path traversal sequences and a code parameter containing malicious PHP code. This results in arbitrary file write capability, which can then be leveraged for remote code execution.

// Security patch in locale/save.php showing the fix
// Source: https://github.com/WWBN/AVideo/commit/57f89ffbc27d37c9d9dd727212334846e78ac21a

if (!isGlobalTokenValid()) {
    $obj->status = 0;
    $obj->error = __("Invalid token");
    die(json_encode($obj));
}

if (empty($_POST['flag'])) {
    forbiddenPage('Flag is empty');
}
$flag = basename($_POST['flag']);
if (empty($flag) || preg_match('/[^a-zA-Z0-9_\-]/', $flag)) {
    $obj->status = 0;
    $obj->error = __("Invalid locale flag");
    die(json_encode($obj));
}
$file = $dir . $flag . ".php";
$myfile = fopen($file, "w") or die("Unable to open file!");
if (!$myfile) {
    $obj->status = 0;

Source: GitHub Commit Update

Detection Methods for CVE-2026-40909

Indicators of Compromise

• Unexpected POST requests to /locale/save.php containing path traversal sequences (../) in request parameters
• Creation of .php files outside the locale/ directory with unexpected timestamps
• Web server access logs showing requests with encoded path traversal patterns (%2e%2e%2f)
• Presence of PHP files with suspicious content in web-accessible directories outside the application's expected locations

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block path traversal patterns in POST parameters
• Monitor file system changes in web server directories for unauthorized PHP file creation
• Review web server access logs for anomalous requests to locale/save.php with suspicious parameter values
• Deploy file integrity monitoring on critical application directories

Monitoring Recommendations

• Enable verbose logging for all requests to administrative endpoints including locale/save.php
• Configure alerts for file creation events in directories where the web server has write access
• Monitor for CSRF attack patterns targeting authenticated administrator sessions
• Implement behavioral analysis to detect unusual administrative activity patterns

How to Mitigate CVE-2026-40909

Immediate Actions Required

• Update WWBN AVideo to a version containing the security fix (commit 57f89ffbc27d37c9d9dd727212334846e78ac21a or later)
• Restrict write permissions on the web server to only necessary directories
• Implement additional access controls on administrative endpoints
• Review existing files in web-accessible directories for any unauthorized PHP files

Patch Information

The vulnerability has been addressed in commit 57f89ffbc27d37c9d9dd727212334846e78ac21a. The fix implements multiple security controls:

1. Global token validation - The patch adds isGlobalTokenValid() check to prevent CSRF attacks
2. Input sanitization - Uses basename() to strip directory components from the flag parameter
3. Character whitelist validation - Applies regex validation to ensure the flag contains only alphanumeric characters, underscores, and hyphens

For more details, see the GitHub Security Advisory GHSA-6rc6-p838-686f.

Workarounds

• Implement web application firewall rules to block requests containing path traversal sequences in POST parameters to locale/save.php
• Restrict access to locale/save.php at the web server level using IP whitelisting or additional authentication
• Configure SameSite=Strict or SameSite=Lax for session cookies to mitigate CSRF attack vectors
• Remove or disable the locale save functionality if not required in your deployment

# Apache configuration to restrict access to locale directory
<Directory "/var/www/html/avideo/locale">
    <Files "save.php">
        # Restrict to specific IP addresses only
        Require ip 192.168.1.0/24
        # Or disable completely if not needed
        # Require all denied
    </Files>
</Directory>