The accidental addition of a data-structure sentinel can cause serious programming logic problems. High to Very High Availability: Generally this error will cause the data structure to not work properly by truncating the data. Pre-design: Use a language or compiler that performs automatic bounds checking. Design: Use an abstraction library to abstract away risky APIs. Not a complete solution. Pre-design through Build: Compiler-based canary mechanisms such as StackGuard, ProPolice, and Microsoft Visual Studio /GS flag. Unless this provides automatic bounds checking, it is not a complete solution. Operational: Use OS-level preventative functionality. Not a complete solution. C C++ char *foo; foo=malloc(sizeof(char)*4); foo[0]='a'; foo[1]='a'; foo[2]=0; foo[3]='c'; printf("%c %c %c %c %c \n",foo[0],foo[1],foo[2],foo[3]); printf("%s\n",foo); Data-structure sentinels are often used to mark structure of the data structure. A common example of this is the null character at the end of strings. Another common example is linked lists which may contain a sentinel to mark the end of the list. It is, of course dangerous, to allow this type of control data to be easily accessible. Therefore, it is important to protect from the addition or modification outside of some wrapper interface which provides safety. By adding a sentinel, one potentially could cause data to be truncated early. 1000 Weakness ChildOf 138 1000 Category ChildOf 461 Addition of data-structure sentinel C C++ (CWE-464)