Address Space Layout Randomization (ASLR) is a Linux security feature that randomizes the location of key areas of a program's memory. This makes it harder for malicious actors to predict the specific areas to target in their attacks.
Enabling ASLR can significantly reduce the risk of specific memory based exploits, common in buffer overflow attacks.
What is address space layout randomization and how does it work?
Address Space Layout Randomization (ASLR) is a security technique that randomizes the memory locations of system and application processes each time they run.
Without ASLR, these processes would occupy predictable memory locations, making them easy targets for attackers. When enabled, ASLR randomly shuffles the memory addresses of crucial components, such as the stack, heap, and executable code, each time a process starts.
By introducing randomness, even if a process is restarted, its memory layout will differ each time, forcing attackers to restart from scratch. This makes it very difficult for attackers to predict specific memory locations, which in turn makes exploiting known vulnerabilities far more challenging.
With ASLR enabled, the operating system will randomly change the position of the stack, reducing the success of memory corruption vulnerabilities.
Why ASLR is important in stopping attacks
ASLR is vital in protecting against malicious attacks which rely on predicting memory locations, such as buffer overflow attacks. These attacks use brute forcing to push data beyond its designated memory boundaries, potentially allowing them to overwrite critical memory areas with malicious code.
However, if the memory addresses are randomized each time a program runs, attackers can no longer predict where to inject their code, significantly reducing the likelihood of a successful exploit.
This technique is especially valuable for preventing brute force attacks, as it forces attackers to guess the randomized address of key components in the system, making repeated attempts far less likely to succeed.
An advantage of ASLR lies in its ability to work with position-independent executables (PIE), which allow code to be loaded at any address without modification, thereby enhancing ASLR's effectiveness. While ASLR provides robust protection, some advanced attackers attempt to bypass ASLR using techniques that exploit the program's behavior or weaknesses in its implementation.
Despite these challenges, the implementation of ASLR in Linux, combined with ASLR support for critical applications, plays a significant role in securing systems against a wide range of memory-based exploits.
How to configure ASLR
Set the following parameter in /etc/sysctl.conf or a file in /etc/sysctl.d/ ending in .conf:
- kernel.randomize_va_space = 2
Example:
| # printf “
kernel.randomize_va_space = 2 ” >> /etc/sysctl.d/60-kernel_sysctl.conf |
Run the following command to set the active kernel parameter:
| # sysctl -w kernel.randomize_va_space=2 |
Note: If these settings appear in a canonically later file, or later in the same file, these
settings will be overwritten
Default value
kernel.randomize_va_space = 2
MITRE ATT&CK Mappings
Techniques / Subtechniques – T1068, T1068.000
Tactics – TA0002
Mitigations – M1050
ASLR and server hardening
Server hardening involves configuring and securing a server to minimize vulnerabilities. ASLR is a fundamental aspect of server hardening, as it reduces predictability in memory layout, making exploitation of memory-based vulnerabilities much harder. When combined with other hardening practices such as disabling unnecessary services, applying regular updates, and enforcing access controls it enhances the server's overall security posture, making it a crucial layer in protecting against attacks.
