How To Protect from Miscalculated Null Termination

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Miscalculated null termination is a common issue, and often difficult to detect. The most common symptoms occur infrequently (in the case of problems resulting from “safe” string functions), or in odd ways characterized by data corruption (when caused by off-by-one errors). The case of an omitted null character is the most dangerous of the possible issues. This will almost certainly result in information disclosure, and possibly a buffer overflow condition, which may be exploited to execute arbitrary code. As for misplaced null characters, the biggest issue is a subset of buffer overflow, and write-what-where conditions, where data corruption occurs from the writing of a null character over valid data, or even instructions. These logic issues may result in any number of security flaws.

  • Requirements specification: The choice could be made to use a language that is not susceptible to these issues.
  • Implementation: Ensure that all string functions used are understood fully as to how they append null characters. Also, be wary of off-by-one errors when appending nulls to the end of strings.