Overview

In C and C++, one may often accidentally refer to the wrong memory due to the semantics of when math operations are implicitly scaled.

Consequences

Often results in buffer overflow conditions.

Exposure period

• Design: Could choose a language with abstractions for memory access.

• Implementation: This problem generally is due to a programmer error.

Platform

C and C++.

Required resources

Any

Severity

High

Likelihood of exploit

Medium

Avoidance and mitigation

• Design: Use a platform with high-level memory abstractions.

• Implementation: Always use array indexing instead of direct pointer manipulation.

• Other: Use technologies for preventing buffer overflows.

Discussion

Programmers will often try to index from a pointer by adding a number of bytes, even though this is wrong, since C and C++ implicitly scale the operand by the size of the data type.

Examples

int *p = x;
char * second_char = (char *)(p + 1);

In this example, second_char is intended to point to the second byte of p. But, adding 1 to p actually adds sizeof(int) to p, giving a result that is incorrect (3 bytes off on 32-bit platforms).

If the resulting memory address is read, this could potentially be an information leak. If it is a write, it could be a security-critical write to unauthorized memory - whether or not it is a buffer overflow.

Note that the above code may also be wrong in other ways, particularly in a little endian environment.