The ext4_valid_block_bitmap function in fs/ext4/balloc.c in the Linux kernel through 4.15.15 allows attackers to cause a denial of service (out-of-bounds read and system crash) via a crafted ext4 image because balloc.c and ialloc.c do not validate bitmap block numbers.
http://openwall.com/lists/oss-security/2018/03/29/1
https://bugzilla.kernel.org/show_bug.cgi?id=199181
https://bugzilla.redhat.com/show_bug.cgi?id=1560782
https://lists.debian.org/debian-lts-announce/2018/06/msg00000.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00015.html
https://lists.debian.org/debian-lts-announce/2018/07/msg00016.html
https://usn.ubuntu.com/3676-1/
https://usn.ubuntu.com/3676-2/
https://usn.ubuntu.com/3752-1/
https://usn.ubuntu.com/3752-2/
https://usn.ubuntu.com/3752-3/