Amazon Linux AMI Security Advisory: ALAS-2015-578
Advisory Release Date: 2015-08-17 12:23 Pacific
Multiple flaws were found in the way httpd parsed HTTP requests and responses using chunked transfer encoding. A remote attacker could use these flaws to create a specially crafted request, which httpd would decode differently from an HTTP proxy software in front of it, possibly leading to HTTP request smuggling attacks.
Run yum update httpd to update your system.