Cross-site request forgery In wwbn/avideo
Description
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']);...
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
Victim logs into the AVideo instance (e.g., https://victim.example.com). PHPSESSID is set with SameSite=None; Secure.
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>...
Victim visits the attacker page in the same browser. The form auto-submits. The browser sends the POST with the victim's session cookie.
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).
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)); }...
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.
Mitigation
Update Impact
Minimal update. May introduce new vulnerabilities or breaking changes.
Ecosystem | Package | Affected version |
|---|---|---|
 packagist | wwbn/avideo |
Aliases
References