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Stack Protector

Question Text​

For the support/memory-security/bo_write_practice executable we are not able overwrite the s variable no matter the input. Why is that?

Question Answers​

  • s needs to be declared after buffer.
  • when using the stack canary, the buffer is always placed right below it.

  • due to ASLR, the address of s is random.

  • the stack canary makes it impossible to overwrite local variables.

Feedback​

When using the canary, to minimize the damage a buffer overflow could cause, the buffers are always placed right below the canary. By doing so, a buffer overflow will not overwrite anything. However, it is still possible to overwrite other local buffers, provided that a function declares more than 1 array or if we use the pointer directly.