Format String Bug Exploration

The Format String vulnerability significantly introduced in year 2000 when remote hackers gain root access on host running FTP daemon which had anonymous authentication mechanism. This was an entirely new tactics of exploitation the common programming glitches behind the software, and now this deadly threat for the software is everywhere because programmers inadvertently used to make coding loopholes which are targeting none other than Format string attack. The format string vulnerability is an implication of misinterpreting the stack for handling functions with variable arguments especially in Printf function, since this article demonstrates this subtle bug in C programming context on windows operating system. Although, this class of bug is not operating system–specific as with buffer overflow attacks, you can detect vulnerable programs for Mac OS, Linux, and BSD. This article drafted to delve deeper at what format strings are, how they are operate relative to the stack, as well as how they are manipulated in the perspective of C programming language.


To be cognizance with the format string bug explained in this article, you will require to having rudimentary knowledge of the C family of programming languages, as well as a basic knowledge of IA32 assembly over window operating system, by mean of visual studio development editor. Moreover, know-how about ‘buffer overflow’ exploitation will definitely add an advantage.


The format string bug was first explained in June 2000 in a renowned journal. This notorious exploitation tactics enable a hacker to subvert memory stack protections and allow altering arbitrary memory segments by unsolicited writing over there. Overall, the sole cause behind happening is not to handle or properly validated the user-supplied input. Just blindly trusting the used supplied arguments that eventually lead to disaster. Subsequently, when hacker controls arguments of the Printf function, the details in the variable argument lists enable him to analysis or overwrite arbitrary data. The format string bug is unlike buffer overrun; in which no memory stack is being damaged, as well as any data are being corrupted at large extents. Hackers often execute this attack in context of disclosing or retrieving sensitive information from the stack for instance pass keys, cryptographic privates keys etc.

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