The ext4_fill_super function in fs/ext4/super.c in the Linux kernel through 4.9.8 does not properly validate meta block groups, which allows physically proximate attackers to cause a denial of service (out-of-bounds read and system crash) via a crafted ext4 image.
https://github.com/torvalds/linux/commit/3a4b77cd47bb837b8557595ec7425f281f2ca1fe
http://www.openwall.com/lists/oss-security/2017/02/05/3