Previously discussed numerous times on HN, like: https://news.ycombinator.com/item?id=48130519

Whether this is a backdoor or not boils down to whatever your usual proclivities about "bug or backdoor" are; it's not like "if microsoft = 1 hack bitlocker" like the tech press seem to love to report.

This is a bug in the NTFS transaction log replay functionality in the Windows Recovery Environment WinRE, where it will read NTFS transaction logs from an external volume and apply them to the mounted filesystem. This allows the attacker to perform an authentication bypass against WinRE. With BitLocker without PIN or Password, _any_ authentication bypass becomes a disk encryption bypass, since the disk is unsealed by the bootloader (this architectural "flaw" is true for Linux with the same configuration, as well, like Ubuntu installed with their newish Hardware Disk Encryption checkbox in the installer).

In lieu of additional evidence, whether you think the NTFS transaction log issue is a planted backdoor or a simple enumeration bug depends on your conspiracy theory level, like most things in exploit development. To me, it seems like a plausible bug. The weaknesses in boot-time unseal are well known and obvious and this is just one of many, so I don't see it as an earth-shattering revelation, although it is a fun bug.

It's very strange that the same component exists in Windows without the issue, though. Like the author, I'm finding it difficult to come up with reasons why they'd be different.