VMware Tools Denial of Service

When utilizing shared folder functionality via vmware-tools on macOS guests, the HGFS implementation does not use adequate bounds checking when replacing illegal characters in a filename.

When sharing files with filenames containing characters that will be escaped by HGFS, it is possible to cause a stack overflow within the kernel extension installed on the guest ( com.vmware.kext.vmhgfs ), which causes the guest to crash. For example, the HGFS implementation for macOS considers colons to be an illegal character. When processing these files from shared folders (including network shares), vmware-tools escapes and replaces illegal characters, which effectively turns 1 character into 2 on the guest VM. If a filename exceeds the filesystem limitation, the guest will experience kernel panic.

As far as we are able to determine, there is no security impact beyond a Denial-of-Service condition via crashing the guest. While the end result is a stack overflow in the kernel extension, we were unable to control this in any meaningful or exploitable way.