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"

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".