Memory Leak

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Abstract

Memory is allocated but never freed.

Description

Memory leaks have two common and sometimes overlapping causes:

• Error conditions and other exceptional circumstances.
• Confusion over which part of the program is responsible for freeing the memory

Most memory leaks result in general software reliability problems, but if an attacker can intentionally trigger a memory leak, the attacker might be able to launch a denial of service attack (by crashing the program) or take advantage of other unexpected program behavior resulting from a low memory condition [1].

Examples

The following C function leaks a block of allocated memory if the call to read() fails to return the expected number of bytes:

	char* getBlock(int fd) {
	char* buf = (char*) malloc(BLOCK_SIZE);
	if (!buf) {
	  return NULL;
	}
	if (read(fd, buf, BLOCK_SIZE) != BLOCK_SIZE) {
	  return NULL;
	}
	return buf;
	}

Related Attacks

Category:Denial of Service Attack

References

[1] J. Whittaker and H. Thompson. How to Break Software Security. Addison Wesley, 2003.