Heap Exploitation: Understanding Memory Corruption Attacks

Memory corruption vulnerabilities are among the most dangerous security flaws in modern software. Exploiting these vulnerabilities allows attackers to manipulate a program’s execution, leading to code execution, privilege escalation, or data leaks. One of the most technically sophisticated methods of exploitation is heap exploitation - a technique that targets dynamically allocated memory to gain control over a system.

In this blog, we’ll break down:

• What heap memory is and how it works

• Common heap-based vulnerabilities

• Real-world heap exploitation techniques

• How to mitigate these threats

Understanding the Heap

The heap is a region of a process’s memory used for dynamic allocation. Unlike the stack, which is managed automatically (for function calls and local variables), the heap allows memory to be allocated and freed manually using functions like:

• malloc() and free() in C

• new and delete in C++

Heap memory is widely used in applications that handle large amounts of data or dynamic memory management, such as browsers, databases, and networking applications.

Heap Exploitation

Common Heap Vulnerabilities

• Use-After-Free (UAF)

  • When an application frees a block of heap memory but continues to reference it, an attacker can manipulate that memory region to control execution flow.

	#include <stdio.h>
	#include <stdlib.h>
	int main() {
		char *ptr = (char*)malloc(10);
		free(ptr);  // Memory freed
		strcpy(ptr, "Hacked!"); // Use-after-free vulnerability
		printf("%s\n", ptr);
		return 0;}
	Here, ptr is used after being freed, allowing an attacker to control or overwrite data.

• Heap Buffer Overflow

  • A heap buffer overflow occurs when data is written beyond the allocated memory, potentially corrupting adjacent heap structures. This can lead to function pointer overwrites or adjacent object modification, giving attackers arbitrary code execution.

#include <stdlib.h>
#include <string.h>
int main() {
	char *ptr = (char*)malloc(8);
	strcpy(ptr, "AAAAAAAAAAAAAAAA"); // Overflow beyond allocated 8 bytes
	free(ptr);
	return 0;}	

• Uninitialized Heap Memory Use

  • If a program reads uninitialized heap memory, an attacker may leak sensitive data or influence program behavior unpredictably.

Heap Exploitation Techniques

1. Heap Spraying

   1. Heap spraying is used in browser exploits to predictably place shellcode in memory. The attacker fills large portions of heap memory with controlled data, increasing the chances of hijacking execution.

2. tcache Poisoning (Modern Exploit)

   1. Modern heap allocators like glibc’s malloc use thread-local caching (tcache) for performance improvements. Attackers exploit tcache bins to manipulate the freelist, redirecting memory allocations to controlled addresses.

      Exploit Concept:

      1. Free a chunk twice (double-free)

      2. Modify the freed chunk’s next pointer

      3. Allocate memory to a controlled location

Real-World Heap Exploits

1. Google Chrome RCE (CVE-2021-21220)

   1. A heap buffer overflow in V8, Chrome’s JavaScript engine, allowed remote attackers to achieve arbitrary code execution by exploiting JIT optimizations.

2. Windows SMBGhost (CVE-2020-0796)

   1. A heap overflow in Windows SMBv3 led to remote code execution (RCE), enabling worm attacks similar to WannaCry.

Mitigations and Defenses

• Use Modern Memory-Safe Languages

  • Shift to Rust, Go, or Python instead of C/C++.

• Implement Memory Protections

  • ASLR (Address Space Layout Randomization)

  • DEP (Data Execution Prevention)

  • Stack Canaries & Control Flow Integrity (CFI)

• Enable Hardened Allocators

  • Hardened malloc, jemalloc, tcmalloc reduce heap corruption risks.

• Fuzzing & Static Analysis

  • Tools like AFL++, libFuzzer, and AddressSanitizer detect heap vulnerabilities before attackers do.

Heap exploitation remains one of the most advanced techniques in modern cybersecurity. Understanding heap memory structures, heap-based vulnerabilities, and modern attack techniques is crucial for securing applications against real-world threats.

With memory corruption still being a prime target for attackers, the future of cybersecurity relies on better mitigations, safer programming practices, and continuous research into exploit techniques. Stay updated, stay secure!

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-AJ