The php_handler function in sapi/apache2handler/sapi_apache2.c in PHP before 5.4.40, 5.5.x before 5.5.24, and 5.6.x before 5.6.8, when the Apache HTTP Server 2.4.x is used, allows remote attackers to cause a denial of service (application crash) or possibly execute arbitrary code via pipelined HTTP requests that result in a "deconfigured interpreter."
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.