What is Arbitrary Code Guard (ACG)?

Arbitrary Code Guard: A Crucial Security Component in Modern OS to Combat Sophisticated Cyber Threats

Arbitrary Code Guard (ACG) is a powerful modern cybersecurity feature that is designed to defend systems against arbitrary code execution, a common aspect of malicious software attacks. Arbitrary code execution is a procedure through which an attacker introduces and runs unauthorized code on a targeted system. This typically involves the manipulation of pointer values to divert a program's control flow and execute the attacker's malignant code. Various forms of attacks that capitalize on arbitrary code execution involve SQL Injection, cross-site scripting, as well as remote file inclusions.

ACG offers valuable protection from these threats byboosting system resistance against unauthorized code execution. This security feature has been implemented across several security software tools and platforms including Microsoft's antimalware tool Windows Defender.

Arbitrary Code Guard increases the hurdle for attackers by making memory sections non-writable and non-executable. In other words, it prohibits code from being written into memory and then executed from the same place, which is a conventional technique that exploits arbitrary code execution. With ACG in place, if a part of the memory is designed to be executable, it must remain 'read-only'; if it's aimed to be written to, then it must remain 'execute-never.'

This approach bars a process from generating mutable already executable pages, reallocating read-only pages to become executable, or using schemes similar to JIT (Just in Time) that can make them executable. Limitations are also placed on segments of the code, preventing them from modification even when kernel-mode pointers could otherwise access them. Any code present in a module applying ACG runs as native executables but system APIs that allow altering of these behaviors are disallowed from being utilized.

When it comes to just-in-time compiled scenarios, such as in JavaScript executed in a browser, which require modifiable and executable memory, measures such as Code Integrity Guard have been introduced. Code Integrity Guard (CIG) relies on virtual address descriptor tables to achieve its goals and the cooperation with the ACG substantially increases the security of processes.

One significant implication of ACG is that it changes the fundamental aspect of how certain types of software, particularly interpreters or just-in-time compilers, function, since they are based around the ability to write and execute code in memory. Therefore, adopting this feature for these software types requires significant modifications. In responding to this challenge, Microsoft incorporated a methodical solution in Edge, ensuring all code generation happens in a dedicated process that is not subject to the ACG constraints, hence permitting JIT to function efficiently and safely.

Arbitrary Code Guard represents an innovative leap in cybersecurity defense. It enriches the underlying security structure by configuring how the code operates, altering interactions amongst the executable code, the operating system, and the CPUs. This feature prevents exploitation techniques from running arbitrary code via the buffer overflow vulnerability or other similar methods that write and execute unauthorized code in memory. ACG may confer some limits on certain types of software, but with proper applications and reinforcements from related features such as CIG, these challenges can be considerably mitigated. By barricading the tentacle of non-self code execution, Arbitrary Code Guard offers a palpable enhancement of capability in combating cyber threats, showing its pivotal role within the realm of cybersecurity and antivirus protection.

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