What is address space layout randomization (ASLR)?

Address space layout randomization (ASLR) is a mechanism to protect against buffer overflow attacks. Most exploit attacks need to know the virtual addresses to hijack control. ASLR helps mitigate this by introducing artificial diversity.

It does this by placing base, libraries, heap, and stack at random positions in the address space of a process. This makes the memory layout unpredictable for attacker programs since they do not know where the next instruction lies.

The following diagram illustrates ASLR:

How ASLR works

ASLR is implemented in some form on most operating systems (OSs), including iOS, Android, Windows, macOS, and Linux.

It includes the following system elements:

• Stack

• Library code

• Heap

• Shared memory between different processes

• Command line arguments

ASLR works in conjunction with the virtual memory managerA technique used by operating systems to give the illusion of increased memory by temporarily transferring data from RAM to disk storage. to randomize the location of the elements mentioned above of a program in memory. This randomization occurs every time the program is run, causing the address to vary consistently. This prevents attackers from inserting malicious code, since they can no longer guess the program's address through trial and error.

Limitations of ASLR

While ASLR is a good way to help fortify programs against common buffer exploits, there are a few ways it can prove to be disadvantageous:

• ASLR does not raise warnings when attempts to bypass it occur.

• After a successful attack, ASLR does not give any information about the attack, such as memory accesses or calls to stack.

• Several successful demonstrations have shown the vulnerability of ASLR by predicting the outcome of randomization. However, more robust hardware support can help mitigate this vulnerability.