Amazon Linux AMI Security Advisory: ALAS-2016-639
Advisory Release Date: 2016-01-18 11:00 Pacific
A heap-based buffer overflow flaw was found in the way grep processed certain pattern and text combinations. An attacker able to trick a user into running grep on specially crafted input could use this flaw to crash grep or, potentially, read from uninitialized memory.
Run yum update grep to update your system.