The ZombieLoad attack allows malicious parties access to sensitive data and keys while a computer system performs non-crucial maintenance tasks.
The following is taken from
https://zombieloadattack.com/ :
“While programs normally only see their own data, a malicious program [such as Zombieload] can exploit the fill buffers to get hold of secrets currently processed by other running programs. These secrets can be user-level secrets, such as browser history, website content, user keys, and passwords, or system-level secrets, such as disk encryption keys.”