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According to the C Standard, section 6.2.4, paragraph 2 [ISO/IEC 9899:2011],

The lifetime of an object is the portion of program execution during which storage is guaranteed to be reserved for it. An object exists, has a constant address, and retains its last-stored value throughout its lifetime. If an object is referred to outside of its lifetime, the behavior is undefined. The value of a pointer becomes indeterminate when the object it points to reaches the end of its lifetime.

Attempting to access an object outside of its lifetime can result in undefined behavior and lead to an exploitable vulnerability. (See also undefined behavior 9  of Appendix J in the C Standard.)

Noncompliant Code Example (Static Variables)

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void init_array(char array[]) {
   /* Initialize array */
   return;
}

int main(int argc, char *argv[]) {
   char array[10];
   init_array(array);
   /* ... */
   return 0;
}

Noncompliant Code

In this noncompliant code sample, the function squirrel_away() stores a pointer to local stack variable local into a location pointed to by function parameter ptr_param. Since it can be assumed that the pointer variable to which ptr_param points remains alive upon squirrel_away()'s return, it is illegal for local to go out of scope.

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Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

Related Guidelines

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Bibliography

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