The PDORow implementation in PHP before 5.3.9 does not properly interact with the session feature, which allows remote attackers to cause a denial of service (application crash) via a crafted application that uses a PDO driver for a fetch and then calls the session_start function, as demonstrated by a crash of the Apache HTTP Server.
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.