[mmastrac]

This one? https://nvd.nist.gov/vuln/detail/CVE-2005-0109

Dang: "Hyper-Threading technology, as used in FreeBSD and other operating systems that are run on Intel Pentium and other processors, allows local users to use a malicious thread to create covert channels, monitor the execution of other threads, and obtain sensitive information such as cryptographic keys, via a timing attack on memory cache misses."

Also, found elsewhere:

"According to Linus Torvalds and others on linux-kernel this is a theoretical attack, paranoid people should disable hyper threading"

[cperciva]

Yes. Intel dismissed it at the time, saying that "nobody would ever have untrusted code running on the same hardware on which cryptographic operations are performed".