Can conference papers use the original words in published papers?
I think you can. Some sentences will inevitably be the same in multiple papers. This is, in my eyes, not necessarily plagiarism. Plagiarism is taking &quot;someone else's work or ideas and passing them off as one's own&quot;. What you are doing here is taking somebody else's words that describe work or ideas and passing them off as your own.
That said, in a case like this there is absolutely no reason why you shouldn't just change the sentence to avoid any perception of plagiarism. For example:

Past methods have exposed a new type of hardware vulnerability to covert timing channels [REFs]. Using 'my method' we investigated such vulnerabilities and present them in this work.