An option is to consider is using the std::string template class rather than manipulating buffers directly. In some cases, there are no replacement functions, so re-architecture of your code is advised.įor Microsoft compiler users, consider using functions from the StrSafe library for the sprintf functions: StringCchPrintf, StringCchVPrintf, StringCchPrintfEx, StringCchVPrintfEx, StringCbPrintf, StringVCbPrintf, StringCbPrintEx, or StringCbVPrintEx, depending on character count or byte count.įor gcc users, consider using functions from the libssp library, such as _snprintf_chk.c and _sprintf_chk.c.Īnother option is the Safe CRT functions, such as sprintf_s, _snprintf_s, _snwprintf_s, _vstprintf_s or _vsntprintf_s.Īs well as using safe replacement functions, it's important to check that the destination buffer is the appropriate size. To avoid security issues, it is recommended that you use equivalent safe functions for each category of function when the safe equivalents exist for your compiler. The banned functions should be replaced with more secure versions, or the code should be re-designed to avoid the banned function entirely. it does not fit in the buffer sprintf(buffer, fmtstring) Buffer overflow. I'm not familiar with how good those features are.Prohibiting the use of these banned APIs is a good way to remove a significant number of code vulnerabilities. Buffer overflows have plagued the C/C++ development community for years. GCC, for example, has the ââ-fstack-protectorââ. It should be noted that some compilers can help against these kinds of errors. Since you filled it with, basically, gargabe, the address the CPU jumped to did probably contain byte sequences that, interpreted as program text, cause an invalid memory access (or the address itself was already bad). The run-time error you experience may well be due to an overwritten return address. If you were writing an application that ran under a privileged user account, you'd just have provided an attacker with a first-grade entry to your costumer's system, an ââACEââ hole, if you will. He might use something like the ââNOP sled techniqueâââ to have your application start a ââshellâââ for him. Thereby the attacker mounted a ââbuffer overflowâââ attack. (NB: Better use ââsnprintfâââ if it's available to you). |-| | buf | |-| | (func args) | |-| | (other stuff) | |-| | return address | |-|Ä«y finding out what exactly the offset between ââbufâââ and the return address on the stack is, a malicious user may manipulate input to your application in a way that the ââXXX.âââ string contains an address of the attacker's choosing at just the point where the uncontrolled ââsprintfâââ function will overwrite the return address on the stack. Now consider a stack frame of your function. the address of the instruction that is to be executed after the function returns, is pushed to the stack (among other things, typically). (3) When you call a function, the return address, i.e. (2) Strings expect the characters belonging to that string to be stored so that character n+1 is stored after character n. the smaller the addresses, the more the stack is filled. (1) Your stack typically "grows" backwards, i.e. A minimal PoC: > from ctypes import > omparam(1e300) buffer overflow detected : terminated Aborted I recommend always controlling how much you copy so Id use snprintf with a size argument instead. If your string ââXXX.ââ comes from uncontrolled sources, you are very close to generating a buffer overflow vulnerability. This could potentially cause RCE when a user allows untrusted input in these functions. And what physically happens next, may well be a major security hole. However, the world does not stop simply because someone did not define what exactly should happen next. The buffer overflow happens due to not checking the length of th sprintf() function on line: case d: sprintf(buffer, , self->tag.As other posters have noted, it invokes UB. It makes a lot of sense to consider what happens in your and, more importantly, similar, cases. The buffer have 8 characters space and only 3 free characters left, however, "XXXXXXXX" is 8 characters long.
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