NTFS: unallocated data marked as allocated

No operation on a file is allowed to include unallocated (deleted) data into the user-readable area of that file. Otherwise, an unprivileged program could read data from a deleted file even if such access was forbidden when this file was allocated.

But this is not an issue when dealing with files readable by privileged programs only (because such programs can read allocated and unallocated data from a file system directly). However, allocated files containing pieces of unallocated data are very rare (unlike the slack space, such data is a part of file’s data).

Continue reading “NTFS: unallocated data marked as allocated”

How the $LogFile works?

In the official NTFS implementation, all metadata changes to a file system are logged to ensure the consistent recovery of critical file system structures after a system crash. This is called write-ahead logging.

The logged metadata is stored in a file called “$LogFile”, which is found in a root directory of an NTFS file system.

Currently, there is no much documentation for this file available. Most sources are either too high-level (describing the logging and recovery processes in general) or just contain the layout of key structures without further description.

Continue reading “How the $LogFile works?”

Hibernation and NTFS

One basic rule when dealing with “hibernated” volumes is to never write anything to them from another operating system. Otherwise, when a hibernated operating system is resumed, there will be a difference between what is on a drive and what the operating system considers to be on that drive.

In Linux, the NTFS-3G driver is issuing the following error message when trying to mount a “hibernated” volume in the read-write mode:

Windows is hibernated, refused to mount.
The disk contains an unclean file system (0, 0).
Metadata kept in Windows cache, refused to mount.
Falling back to read-only mount because the NTFS partition is in an
unsafe state. Please resume and shutdown Windows fully (no hibernation
or fast restarting.)

But this rule isn’t enforced in the Windows world. An NTFS volume is automatically mounted in the read-write mode even if it belongs to a hibernated operating system.

Since the fast startup mode, which uses the hibernation feature to restore the state of the kernel and the loaded drivers, is enabled by default in Windows 8.1 & 10 installations running on most modern computers, such behavior can lead to data corruption in a dual-boot configuration or when a system drive is attached to another computer.

From a forensics perspective, this means that hibernation files may contain some important data.

Continue reading “Hibernation and NTFS”