Unintentional pointer scaling

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Vulnerabilities Table of Contents

Description
In C and C++, one may 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

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.

Risk Factors
TBD

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.

Related Attacks

 * Attack 1
 * Attack 2

Related Vulnerabilities

 * Vulnerability 1
 * Vulnerabiltiy 2

Related Controls

 * 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.

Related Technical Impacts

 * Technical Impact 1
 * Technical Impact 2