heap spraying is a classic technique in the world of computer security and exploitation. Let’s break it down in a way that’s clear and intuitive:

🧠 What Is Heap Spraying?

Heap spraying is a method attackers use to increase the chances of successful code execution during an exploit — especially when targeting memory corruption vulnerabilities like buffer overflows.

It involves filling the heap (a region of memory used for dynamic allocation) with malicious code or payloads, so that when a vulnerability is triggered, the program is more likely to jump to and execute that code.

🧪 How It Works (Step-by-Step)

1. Spray the Heap
   The attacker allocates large blocks of memory filled with NOP sleds (no-operation instructions) followed by shellcode (malicious code).

2. Trigger a Vulnerability
   A bug like a buffer overflow or use-after-free is exploited to redirect the program’s execution flow to an address in memory.

3. Land on the Payload
   Because the heap is “sprayed” with many copies of the payload, the chances of landing on one are high — even if the exact address isn’t known.

🧰 Common Use Cases

🧱 What’s in a Heap Spray?

• NOP sled: A long sequence of NOP instructions (e.g., 0x90 in x86) that safely leads to the shellcode.
• Shellcode: The actual malicious code — could open a reverse shell, download malware, etc.
• Repetition: Thousands or millions of copies to blanket the heap.

🛡️ Defense Against Heap Spraying

Modern systems use several techniques to mitigate heap spraying:

⚠️ Ethical Note

Heap spraying is a real-world exploitation technique used in both offensive and defensive security. Understanding it is crucial for:

• Malware analysts
• Security researchers
• Penetration testers

But it should only be studied and used in ethical, legal contexts — like lab environments or authorized testing.

 let’s explore both a simplified example of a heap spray in JavaScript and how modern browsers defend against it. This will give you a full picture of how the attack works and how it’s mitigated today.

🧪 Simplified JavaScript Heap Spray Example

This is a conceptual demo — not a working exploit — just to show how heap spraying might look in older browsers like Internet Explorer:

// Create a NOP sled (0x90 is NOP in x86)
var sled = unescape("%u9090%u9090");

// Shellcode placeholder (in real attacks, this would be actual malicious code)
var shellcode = unescape("%u4141%u4242%u4343%u4444");

// Spray the heap with NOP sled + shellcode
var spray = sled;
while (spray.length < 0x1000) spray += sled;

spray += shellcode;

// Fill memory with sprayed blocks
var memory = [];
for (var i = 0; i < 1000; i++) {
    memory[i] = spray + spray;
}

🧠 What’s Happening Here?

• unescape() is used to encode binary data into JavaScript strings.
• The script builds a large block of memory filled with NOPs and shellcode.
• It repeats this block many times to increase the chance of hitting it during an exploit.

This technique was often used in older browsers that didn’t have strong memory protections.

🛡️ How Modern Browsers Defend Against Heap Spraying

1. ASLR (Address Space Layout Randomization)

• Randomizes memory addresses every time a program runs.
• Makes it hard for attackers to predict where their sprayed payload will land.

2. DEP (Data Execution Prevention)

• Marks certain memory regions (like the heap) as non-executable.
• Even if shellcode lands there, it won’t run.

3. JIT Hardening

• Just-In-Time (JIT) compilers in browsers are hardened to prevent predictable memory layouts.
• Prevents attackers from abusing JIT-generated code for spraying.

4. Sandboxing

• Each browser tab or plugin runs in its own isolated process.
• Limits the impact of a successful exploit.

5. Heap Integrity Checks

• Browsers implement checks to detect abnormal memory behavior.
• Can block or crash suspicious scripts before they do damage.

🔐 Summary