Wrap-around error

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Overview

Wrap around errors occur whenever a value is incriminated past the maximum value for its type and therefore "wraps around" to a very small, negative, or undefined value.

Consequences

  • Availability: Wrap-around errors generally lead to undefined behavior, infinite loops, and therefore crashes.
  • Integrity: If the value in question is important to data (as opposed to flow), simple data corruption has occurred. Also, if the wrap around results in other conditions such as buffer overflows, further memory corruption may occur.
  • Access control (instruction processing): A wrap around can sometimes trigger buffer overflows which can be used to execute arbitrary code. This is usually outside the scope of a program's implicit security policy.

Exposure period

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Design: If the flow of the system, or the protocols used, are not well defined, it may make the possibility of wrap-around errors more likely.
  • Implementation: Many logic errors can lead to this condition.

Platform

  • Language: C, C++, Fortran, Assembly
  • Operating System: Any

Required resources

Any

Severity

High

Likelihood of exploit

Medium

Avoidance and mitigation

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Design: Provide clear upper and lower bounds on the scale of any protocols designed.
  • Implementation: Place sanity checks on all incremented variables to ensure that they remain within reasonable bounds.

Discussion

Due to how addition is performed by computers, if a primitive is incremented past the maximum value possible for its storage space, the system will fail to recognize this, and therefore increment each bit as if it still had extra space.

Because of how negative numbers are represented in binary, primitives interpreted as signed may "wrap" to very large negative values.

Examples

See the Examples section of the problem type Integer overflow for an example of wrap-around errors.

Related problems

  • Integer overflow
  • Unchecked array indexing

Categories