Amazon Linux AMI Security Advisory: ALAS-2017-851
Advisory Release Date: 2017-06-22 22:54 Pacific
Apache HTTP Request Parsing Whitespace Defects
It was discovered that the HTTP parser in httpd incorrectly allowed certain characters not permitted by the HTTP protocol specification to appear unencoded in HTTP request headers. If httpd was used in conjunction with a proxy or backend server that interpreted those characters differently, a remote attacker could possibly use this flaw to inject data into HTTP responses, resulting in proxy cache poisoning.(CVE-2016-8743 )
Run yum update httpd to update your system.