SANS Digital Forensics and Incident Response Blog: Tag - cluster chains

A big FAT lie part 2

Last week we looked at the next file in our disk image (next file according to the output from fls). We saw that though the file was 15585 bytes, istat reported only a single sector for the file. Based on our cluster/sector size of 512 bytes, the file should have occupied 31 sectors (15585/512=30.439..., round up).

We theorized that we may have a broken or missing FAT cluster chain. Knowing the file should occupy 31 clusters, we used the blkstat command to carve out 31 clusters of data beginning at sector 834. We found only nulls.

At this point, most sane investigators probably would have reached for their favorite


Rebuilding FAT cluster chains

For those reading this entry and not familiar with the others in the series, a brief bit of background is in order. This post is the fourth in a series about the FAT file system. We have a disk image taken from a suspect's USB key, but some of the metadata has been modified to make getting at the evidence more difficult, though only slightly. We're attempting to undo the modifications our suspect has made and restore the image to its unaltered state.

I did a little digging over the weekend and discovered a couple links that may be of interest to those playing along at home. First, Mike Murr, of Code-X Technologies and, has covered some aspects concerning our image on his blog