Buffer overflow protection: Difference between revisions

Revision as of 23:57, 19 January 2023

Revision as of 09:50, 23 January 2023

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''Random canaries'' are randomly generated, usually from an [[entropy (computing)|entropy]]-gathering [[daemon (computer software)|daemon]], in order to prevent an attacker from knowing their value. Usually, it is not logically possible or plausible to read the canary for exploiting; the canary is a secure value known only by those who need to know it—the buffer overflow protection code in this case.

Normally, a random canary is generated at program initialization, and stored in a global variable. This variable is usually padded by unmapped pages, so that attempting to read it using any kinds of tricks that exploit bugs to read off RAM cause a segmentation fault, terminating the program. It may still be possible to read the canary, if the attacker knows where it is, or can get the program to read from the stack.

===Random XOR canaries===