The do_anonymous_page function in mm/memory.c in the Linux kernel before 2.6.27.52, 2.6.32.x before 2.6.32.19, 2.6.34.x before 2.6.34.4, and 2.6.35.x before 2.6.35.2 does not properly separate the stack and the heap, which allows context-dependent attackers to execute arbitrary code by writing to the bottom page of a shared memory segment, as demonstrated by a memory-exhaustion attack against the X.Org X server.
The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment.