Vulnerabilities > CVE-2016-9377 - Incorrect Calculation vulnerability in XEN

An attacker exploits a data structure shared between multiple applications or an application pool to affect application behavior. Data may be shared between multiple applications or between multiple threads of a single application. Data sharing is usually accomplished through mutual access to a single memory location. If an attacker can manipulate this shared data (usually by co-opting one of the applications or threads) the other applications or threads using the shared data will often continue to trust the validity of the compromised shared data and use it in their calculations. This can result in invalid trust assumptions, corruption of additional data through the normal operations of the other users of the shared data, or even cause a crash or compromise of the sharing applications.

An attacker takes advantage of the structure of integer variables to cause these variables to assume values that are not expected by an application. For example, adding one to the largest positive integer in a signed integer variable results in a negative number. Negative numbers may be illegal in an application and the application may prevent an attacker from providing them directly, but the application may not consider that adding two positive numbers can create a negative number do to the structure of integer storage formats.

This attack involves an attacker manipulating a pointer within a target application resulting in the application accessing an unintended memory location. This can result in the crashing of the application or, for certain pointer values, access to data that would not normally be possible or the execution of arbitrary code. Since pointers are simply integer variables, Integer Attacks may often be used in Pointer Attacks.