There is only one file type that uses the .KRAB extension:
GandCrab V4 Ransomware Encrypted File
A KRAB file is a file encrypted by the GandCrab V4 virus, a trojan horse utilized by cybercriminals. It contains a user's file, such as a .XLSX or .MP4 file, encrypted with the Salsa20 algorithm. KRAB files became prevalent in July 2018 and are similar to .GDCB files.
The GandCrab V4 virus is ransomware, where the purpose of the virus is to take your computer files hostage and force you to pay the perpetrator (typically via bitcoin) to unlock your files. The virus is a trojan horse that is commonly introduced through fake blogs that provide cracked software. Users download and install the software, which is actually the GandCrab V4 virus that scrambles, renames, and encrypts the user's files. The virus then generates a .TXT ransom note (KRAB-DECRYPT.txt) informing you of the takeover and what you need to do to recover your files.
There is no program currently available to effectively restore your files. If you backup your files you can execute a full system restore. Otherwise, the only known way to decrypt your infected files is to pay the perpetrator for the private key and decrypt program.
filename.ext.KRAB - Encrypted files have the KRAB extension appended to the end of the file. For example, sample.xls becomes sample.xls.KRAB.
Updated: June 6, 2018