Editing Exec Shield (section)

{{Short description|Project aiming to reduce the risk of attacks on Linux systems}}
{{Refimprove|date=September 2007}}
'''Exec Shield''' is a project started at [[Red Hat]], Inc in late 2002 with the aim of reducing the risk of worm or other automated remote attacks on Linux systems. The first result of the project was a [[computer security|security]] patch for the [[Linux (kernel)|Linux kernel]] that emulates an [[NX bit]] on [[x86]] [[Central processing unit|CPUs]] that lack a native NX implementation in hardware. While the Exec Shield project has had many other components, some people refer to this first patch as Exec Shield.

The first Exec Shield patch attempts to flag data memory as non-executable and program memory as non-writeable. This suppresses many [[Exploit (computer science)|security exploits]], such as those stemming from [[buffer overflow]]s and other techniques relying on overwriting data and inserting code into those structures.  Exec Shield also supplies some [[address space layout randomization]] for the [[mmap]]() and heap base.

The patch additionally increases the difficulty of inserting and executing [[shellcode]], rendering most exploits ineffective. No application recompilation is necessary to fully utilize exec-shield, although some applications ([[Mono (software)|Mono]], [[Wine (software)|Wine]], [[XEmacs]], [[Mplayer]]) are not fully compatible.

Other features that came out of the Exec Shield project were the [[Position-independent code|Position Independent Executables]] (PIE), the address space randomization patch for Linux kernels, a wide set of glibc internal security checks that make heap and format string exploits near impossible, the GCC [[Fortify Source]] feature, and the port and merge of the GCC [[Buffer overflow protection#GCC Stack-Smashing Protector .28ProPolice.29|stack-protector]] feature.