https://www.bleepingcomputer.com/news/security/microsoft-releases-info-on-protecting-bitlocker-from-dma-attacks/

Soon after research was released that BitLocker drives could be decrypted using SSD hardware encryption flaws, Microsoft  released a support bulletin describing how to protect BitLocker from 1394 & Thunderbolt DMA attacks.

1394 and Thunderbolt devices are capable of Direct Memory Access, or DMA, which unless restricted, allows these devices to read and write to the entire system memory of the computer without utilizing the computer's processor.