The vulnerabilities include a filtration of the SSL keys the machines use to communicate and authenticate with the central counting servers.
https://twitter.com/stimpyjaycat/status/617180410561339392
In spanish, about some of the vulnerabilities: www.telam.com.ar/notas/201506/110512-a-diez-dias-de-los-comicios-portenos-descubren-filtraciones-de-seguridad-en-el-sistema-de-voto-electronico.html