Summary

Type: Classic shell-metacharacter injection. The YPTSocket notification branch in plugin/Live/on_publish.php builds an execAsync() command line by string concatenation, single-quoting each argument but never calling escapeshellarg(). A ' in any of the three interpolated values ($users_id, $m3u8, $obj->liveTransmitionHistory_id) closes the quoted token and lets the attacker append arbitrary commands.
File: plugin/Live/on_publish.php, line 267.
Root cause: the developer wrapped each variable in literal single quotes ('$users_id', '$m3u8', '$obj->liveTransmitionHistory_id') believing this provides shell-quoting. PHP single-quoted-into-shell is not safe quoting; it is just two literal quote characters that the shell pairs greedily. Any embedded ' closes the outer string and resumes interpretation in the shell. The rest of the AVideo codebase already calls escapeshellarg() (137 call sites across the project) for ffmpeg invocations, so the safe primitive is well-known to the project; it was simply omitted from this branch. The endpoint is web-reachable (no .htaccess rule restricts on_publish.php, no REMOTE_ADDR check), so the trigger is a direct HTTP POST without going through nginx-rtmp.

Affected Code

File: plugin/Live/on_publish.php, lines 256-271.

if (AVideoPlugin::isEnabledByName('YPTSocket')) {
    $array = setLiveKey($lth->getKey(), $lth->getLive_servers_id());
    @ob_clean();
    _ob_start();
    $lth = new LiveTransmitionHistory($obj->liveTransmitionHistory_id);
    $m3u8 = Live::getM3U8File($lth->getKey(), false, true);          // value-carrying URL: contains the stream key verbatim
    $users_id = $obj->row['users_id'];
    $liveTransmitionHistory_id = $obj->liveTransmitionHistory_id;
    if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
        include "{$global['systemRootPath']}plugin/Live/on_publish_socket_notification.php";
    } else {
        $command = get_php(). " {$global['systemRootPath']}plugin/Live/on_publish_socket_notification.php '$users_id' '$m3u8' '{$obj->liveTransmitionHistory_id}'";  // <-- BUG: literal quotes, no escapeshellarg
        $pid = execAsync($command);                                  // sink: shell exec
    }
}

Live::getM3U8File($key, false, true) (Live.php:1337-1350 -> Live.php:4845-4889) returns "{$playerServer}{$uuid}.m3u8" (or "{$playerServer}{$uuid}/index.m3u8") where $uuid = $this->getKeyWithIndex(...) is the stream key string read straight out of the live_transmitions table. There is no character normalisation between database read and command construction.

Why it's wrong: '$m3u8' is not shell quoting. PHP interpolates $m3u8 into the string between two literal ' characters. The shell then tokenises the result. If $m3u8 contains ' itself, the shell sees '…' followed by <attacker bytes> followed by another ', which forms two adjacent quoted strings concatenated with whatever the attacker put between them. Embedded ;, backticks, $(), &&, |, or \n then run as shell commands. The fix is escapeshellarg(), which AVideo already uses 137 times in ffmpeg invocations (e.g. getVideos.php:1069, videos.json.php, aVideoEncoder.json.php); this branch simply forgot it.

Exploit Chain

1. Attacker authenticates and arranges for one of the command variables to contain '. Under the current code the readily available primitive is a canStream user supplying a stream key via the persistence path (saveLive.php's $_REQUEST['key'] is written verbatim to live_transmitions.key). State: a row exists with key = "evilkey';id>/tmp/pwn;#".
2. Attacker POSTs directly to https://target/plugin/Live/on_publish.php (the file is web-served, no IP restriction) with body:

   name=evilkey';id>/tmp/pwn;#
   p=<md5(attacker_password)>
   tcurl=rtmp://target/live
   addr=1.2.3.4
   

   on_publish.php:117 runs preg_replace("/[&=]/", '', $_POST['name']) — only &/= are stripped, so ';id>/tmp/pwn;# survives. Lines 143-163 confirm $_GET['p'] === $user->getPassword() (the attacker is themself, knows their own MD5), persist a LiveTransmitionHistory row with the poisoned key, and set $obj->error = false. State: authorisation gate passed.
3. Line 261 calls Live::getM3U8File($lth->getKey(), false, true), returning "https://server/live/evilkey';id>/tmp/pwn;#.m3u8". State: $m3u8 carries the injection payload.
4. Line 267 builds the command string by concatenation:

   php /var/www/AVideo/plugin/Live/on_publish_socket_notification.php '7' 'https://server/live/evilkey';id>/tmp/pwn;#.m3u8' '42'
   

   Shell tokenisation sees: php, …/on_publish_socket_notification.php, '7', 'https://server/live/evilkey' (the attacker's ' closed the second quote), then operator ;, then command-2 id>/tmp/pwn, then ;, then #.m3u8' '42' (everything after # is a comment). State: the shell has parsed two real commands.
5. Line 269 execAsync($command) spawns the shell, which runs the secondary command id>/tmp/pwn as the AVideo PHP-FPM/Apache user. State: arbitrary OS command execution with the privileges of the web-server runtime user.
6. Final state: the attacker reads /tmp/pwn, swaps the payload for a reverse shell, exfiltrates videos/configuration.php (database password and root URL), drops a webshell into the upload tree, or pivots to other plugin credentials (PayPal/Stripe API keys, AWS keys for the CDN plugin, OpenAI key for the AI plugin).

Security Impact

Severity: sec-high. Pre-auth-friendly remote code execution: the only prerequisite is that the attacker can place a ' into one of the three command-line variables, which on a streaming platform means a single low-privilege account.
Attacker capability: with one canStream account and two HTTP requests, the attacker executes arbitrary shell commands as the AVideo runtime user. From there: read database credentials, exfiltrate user data, write a webshell into a publicly-served path, pivot to plugin credentials, persist via cron, or escalate via any local sudoers entries.
Preconditions: AVideo deployment with Live and YPTSocket plugins enabled (the standard live-streaming bundle); attacker can reach /plugin/Live/on_publish.php over the network; a value containing ' is reachable into users_id, m3u8, or liveTransmitionHistory_id (the current code lets canStream users supply such a value via the stream-key persistence path).
Differential: source-inspection-verified end-to-end. The shell-tokenising behaviour of '…'…'…' is reproducible offline:

$ s="php /a/b.php '7' 'https://s/live/evilkey';id>/tmp/pwn;#.m3u8' '42'"
$ rm -f /tmp/pwn; bash -c "$s" 2>/dev/null; ls -l /tmp/pwn
-rw-r--r-- 1 user user N <date> /tmp/pwn        # injected `id` ran, output captured

The patched build (with the suggested escapeshellarg() fix below applied) constructs php /a/b.php '7' 'https://s/live/evilkey'\''id>/tmp/pwn;#.m3u8' '42', which the shell parses as a single argument containing the literal characters; the second command never runs.

Suggested Fix

Use escapeshellarg() on every variable interpolated into the command string. This matches established project conventions (137 other call sites for ffmpeg invocations).

--- a/plugin/Live/on_publish.php
+++ b/plugin/Live/on_publish.php
@@ -264,7 +264,11 @@
         if (strtoupper(substr(PHP_OS, 0, 3)) === 'WIN') {
             include "{$global['systemRootPath']}plugin/Live/on_publish_socket_notification.php";
         } else {
-            $command = get_php(). " {$global['systemRootPath']}plugin/Live/on_publish_socket_notification.php '$users_id' '$m3u8' '{$obj->liveTransmitionHistory_id}'";
+            $command = get_php()
+                . ' ' . escapeshellarg($global['systemRootPath'] . 'plugin/Live/on_publish_socket_notification.php')
+                . ' ' . escapeshellarg((string) $users_id)
+                . ' ' . escapeshellarg((string) $m3u8)
+                . ' ' . escapeshellarg((string) $obj->liveTransmitionHistory_id);
             _error_log("NGINX Live::on_publish YPTSocket start  ($command)");
             $pid = execAsync($command);
         }

Defence-in-depth: on_publish.php is the nginx-rtmp webhook and should not be reachable from the public Internet. Add an .htaccess/nginx location rule restricting the file to 127.0.0.1 and any configured RTMP server IPs. That blocks the trigger path independently of the sanitisation work.

References

• GHSA-xw67-cg5f-4m2r