How To Protect from Integer Overflow

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Integer overflows are for the most part only problematic in that they lead to issues of availability. Common instances of this can be found when primitives subject to overflow are used as a loop index variable. In some situations, however, it is possible that an integer overflow may lead to an exploitable buffer overflow condition. In these circumstances, it may be possible for the attacker to control the size of the buffer as well as the execution of the program. Recently, a number of integer overflow-based, buffer-overflow conditions have surfaced in prominent software packages. Due to this fact, the relatively difficult to exploit condition is now more well known and therefore more likely to be attacked. The best strategy for mitigation includes: a multi-level strategy including the strict definition of proper behavior (to restrict scale, and therefore prevent integer overflows long before they occur); frequent sanity checks; preferably at the object level; and standard buffer overflow mitigation techniques.

  • Pre-design : Use a language or compiler that performs automatic bounds checking.
  • Design : Use of sanity checks and assertions at the object level. Ensure that all protocols are strictly defined, such that all out of bounds behavior can be identified simply.
  • Pre-design through Build: Canary style bounds checking, library changes which ensure the validity of chunk data, and other such fixes are possible but should not be relied upon.
  • Implementation: Sanity checks should be performed on all calculated values used for memory allocation, as an index, or for pointer arithmetic.
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