A buffer is a portion of memory set aside for a specific purpose, and a buffer overflow occurs when a write operation into the buffer keeps going past the end. This can cause data corruption and program overwrites nearby data that was not supposed to be changed by the write. In C, the Core Foundation representation of a string, CFStringRef, can be used to manipulate strings.
A buffer overflow attack is the exploitation of a buffer overflow vulnerability, typically by a malicious actor who wants to gain access or information. The easiest way to identify the buffer overflow and learn how to exploit it is to own the buffer and control the user input character by character.
In this example, a long input string can overflow the buffer, leading to data corruption. The file badfile is controlled by a normal user, and if you read larger than the buffer size, the following memory addresses will be overwritten. This is what causes buffer overflow.
To implement a shellcode-based buffer overflow attack against a program executable, first find the getName function. If you read larger than the buffer size, the following memory addresses will be overwritten, which is allowed and causes buffer overflow.
In summary, a buffer overflow occurs when a program writes to memory beyond the allocated address, clobbering nearby data that was not intended by the write. To prevent this, it is essential to use proper memory management and avoid using long input strings in programs.
📹 coding in c until my program is unsafe
C Programming isn’t all it’s cracked up to be boys and girls. IT TAKES GUTS. GRIT. DETERMINATION. SELF HATE. LUST?
How do I fix buffer overflow detected?
To prevent buffer overflow attacks, use languages with built-in protection mechanisms like C, Java, JavaScript, and PERL. Avoid standard library functions without bounds-checks in C/C++ languages. Use special security procedures to minimize vulnerabilities. Review custom codes and codes that accept user inputs via HTTP requests. Ensure input sizes and bounds are checked. Proactively identify and fix coding errors.
Modern Operating Systems offer runtime protections like Structured Exception Handler Overwrite Protection (SEHOP) and Address Space Randomization (ASLR), which randomly moves around data location address spaces, making it nearly impossible to execute buffer overflow attacks without knowing the executable code’s location.
What is buffer overflow in string?
A buffer overflow condition occurs when a program tries to put more data in a buffer than it can hold or attempts to put data in a memory area past a buffer. This can corrupt data, crash the program, or execute malicious code. Buffer overflow is the most known form of software security vulnerability, and it is common in both legacy and newly-developed applications. The problem is due to the wide variety of ways buffer overflows can occur and the error-prone techniques used to prevent them.
Do buffer overflows still work?
Buffer overflows are a significant security issue that can be exploited by attackers to corrupt software. In 2014, the “heartbleed” threat exposed hundreds of millions of users to a buffer overflow vulnerability in SSL software. An attacker can deliberately feed a crafted input into a program, causing it to store it in a buffer that isn’t large enough, overwriting portions of memory connected to the buffer space.
If the program’s memory layout is well-defined, the attacker can overwrite areas known to contain executable code, replacing it with their own executable code, which can drastically change the program’s intended functionality. For example, if the overwritten memory contains a pointer pointing to an exploit payload, the attacker’s code could replace that pointer with another one, transferring control of the entire program.
Is buffer over read the same as buffer overflow?
Buffer over-reads are the opposite of buffer overflows, where a program requests data from outside the buffer, potentially causing it to crash or behave strangely. This can also be a mechanism for breaching security. For example, if a program reads beyond the buffer’s bounds, it may access unrelated confidential data. Buffer over-reads have been a significant cause of real-world cyber-attacks, such as the Heartbleed vulnerability in OpenSSL. Examples of damage from Heartbleed include:
What are the strategies for buffer overflow?
A buffer overflow represents a common vulnerability in software security. It can be prevented through a variety of measures, including auditing code, providing training, utilizing compiler tools, employing safe functions, patching web and application servers, and scanning applications. This error results in system memory being exposed to a malicious threat. The use of comprehensive templates can assist organizations in remaining proactive in the face of such threats.
What is the difference between buffer over-read and buffer overflow?
Buffer over-reads are the opposite of buffer overflows, where a program requests data from outside the buffer, potentially causing it to crash or behave strangely. This can also be a mechanism for breaching security. For example, if a program reads beyond the buffer’s bounds, it may access unrelated confidential data. Buffer over-reads have been a significant cause of real-world cyber-attacks, such as the Heartbleed vulnerability in OpenSSL. Examples of damage from Heartbleed include:
What is an example of a buffer overflow?
A buffer overflow attack is a method used by attackers to overwrite the memory of an application, altering its execution path and potentially damaging files or exposing private information. This can be done by introducing extra code or sending new instructions to gain access to IT systems. If the attacker knows the program’s memory layout, they can intentionally feed input that the buffer cannot store and overwrite areas holding executable code, replacing it with their own code.
There are two types of buffer overflow attacks: stack-based and heap-based. Stack-based attacks leverage stack memory during function execution, while heap-based attacks flood memory space beyond current runtime operations.
What causes a buffer overflow answer?
Buffers are memory storage regions that temporarily hold data during data transfer. A buffer overflow occurs when the volume of data exceeds the buffer’s storage capacity, leading to the program overwriting adjacent memory locations. For instance, a buffer for log-in credentials may write excess data past the buffer boundary if an input exceeds the expected 8 bytes. Buffer overflows can affect all types of software and can result from malformed inputs or failure to allocate enough space for the buffer. If the transaction overwrites executable code, it can cause unpredictable behavior, incorrect results, memory access errors, or crashes.
Why is buffer overflow bad?
Buffer overflows are common issues in software that can lead to unpredictable behavior, memory access errors, or crashes. Attackers exploit these issues by overwriting the memory of an application, altering its execution path, causing damage to files or exposing private information. They can introduce extra code or send new instructions to gain access to IT systems. If they know the program’s memory layout, they can intentionally feed input that the buffer cannot store and overwrite areas holding executable code, replacing it with their own code. For instance, they can overwrite a pointer to an exploit payload to gain control over the program.
What is read buffer overflow?
A buffer over-read or out-of-bounds read is an anomaly where a program overruns the buffer’s boundary while reading data, violating memory safety. This can be triggered by malicious inputs or programming errors alone. Buffer over-reads can result in erratic program behavior, memory access errors, incorrect results, crashes, or system security breaches. They are the basis of many software vulnerabilities and can be exploited to access privileged information.
In some cases, buffer over-reads not caused by malicious input can lead to crashes if they trigger invalid page faults. For example, widespread IT outages in 2024 were caused by an out-of-bounds memory error in cybersecurity software developed by CrowdStrike.
What is buffer overflow vs format string?
Buffer overflow and format string attacks are two types of programming vulnerabilities that can be exploited by attackers. Buffer overflow occurs when a programmer fails to maintain user input between bounds, allowing attackers to write to adjacent memory locations. Format string attacks, on the other hand, involve the inclusion of user-supplied input in the format string argument, allowing attackers to control the location of arbitrary writes. Format strings are essential in C programming to integrate specific formats into output, and format specifiers inform the compiler about processed data.
📹 How To Clear The Input Buffer | C Programming Tutorial
How to clear the standard input buffer in C, as well as why we might need to clear/flush the input buffer. It might seem like fgets(), …
Why the program was not safe: 1. He did not check if argc was equal to 0, 1, or any other number. 2. He did not terminate the program when outside of parameters e.g. if argc > 2, exit program. 3. He used strcpy, which is considered unsafe as it may be used in buffer overflow attacks. Use strncpy instead. Probably missed something.
If you don’t know what the problem is: 1. He didn’t take into account the null terminator, meaning that using that as a string will result in an undefined behavior. 2. He didn’t add any check that ensured the parameter input from the command console would be 2 characters or less (otherwise it would overflow from the array) or any limiter that cut the input within the limits of the array. TLDR: You can easily go beyond the array with the user input which is not gonna end well.
Reminds me of team project at university where we all worked on different parts of the program. When we met up to put it all together, we quickly realized one of us did NOT compile their part at all from the very beginning. Months. It says it all when you see comparing strings like: if (variable == “DOG”)…
For those who dont get it, there were a few problems. First he did not check in argc if there even were an argv – potentially unsafe program. Second he did not make sure the string he is copying is actually three bytes – incase the string is larger he will overflow the buffer he allocated – potentially unsafe.
General rule for strings in C that I learned in my operating systems class: just use malloc and allocate one extra memory slot for the null terminator. I used to think using the heap was a pain in the ass but in C it actually reduces a lot of issues with seg faults and garbage values overwriting your buffers value.
I appreciate you guys that write C. The only ones I respect more are those that can code in assembly. Never understood all this inter-lingual animosity. That having been said, I’m happy with Python and Java, I just don’t have this in my soul, but I’m glad someone out there does. Edit: Recently started making Android apps with Kivy. One step in the packaging process is to take the Python code and compile it into native C/C++. Every time I watch that part of the stdout, I spare a happy thought for all you C programmers out there. Even Python’s written in C.
C is just like that, such a beautiful language… full of… of… pitfalls and dangers for the young and novice… it is nor even fun to speedrun this sort of thing, since it would boil down to who can type the fastest, no skill required! trust me… as someone who done and still does a lot of bad C(war crime level kind of bad, this is no laughing matter!) and still does, yes… still bad, if not worse…. from buffer overflows to blowing up the memory stack…. I tried to use openbsd libbsd, where we have reallocarray and strlcpy… but it just gets worse… at least I sort of know that is wrong and bad… but I am not sure if what actually works is any good or any safe…
Minor correction: including stdio.h is not including a library. The library is already being implicitly included by your compiler. The header file (stdio.h) just includes the forward declarations. This can be seen clearly if you were to either: a) try to compile your stdio.h including code with -no-std or something b) didn’t include stdio.h, but pasted function prototypes for the functions you’d like to use at the top of your c file (it would still work)
The criticism in this article is valid — I personally find it absurd that strcpy is not removed or even recommended against as of the latest C standard — but as others have pointed out in the comments, it’s kind of a cheap shot because it’s usually very easy to avoid these particular pitfalls. Personally, I think the more compelling case against C is just how much undefined behavior it has, hidden in places that even an experienced C dev may forget about. (Can you name them all without looking it up?) I wrote an example that I don’t think YouTube’ll let me “paste,” so instead I shall just say that it’s in the “bin” at m2w42hGM. A few things to keep in mind as you read it: a) Clang is following all of the relevant parts of the standard to the letter. The C standard says that doing this results in undefined behavior (which is standards-speak for “all bets are off, the implementation can do whatever it wants”). b) This isn’t even a bug in Clang, but rather a consequence of how LLVM models code execution. That model enables some really good optimizations (which is to say, the LLVM devs aren’t just munging up programs for fun) but the onus is still on you, the C dev, to use it correctly. c) Yeah, this is a contrived example, and it’s one that the right static code analysis tools could have pointed out for me, but it’s meant to illustrate the anything-goes nature of UB. But something like it could still happen in the real world: Maybe when I wrote this code, I rationalized that always_true is indeed always true, and I tested it on a different compiler that just happened to produce a program that behaved in the “expected” way, and then I pushed it to Git, and it wasn’t until someone else built it with Clang (perhaps to deploy it!
C is not hard. But Safer C (I’ll just call it that) requires patience and throuroughness. My teacher always said: “Functionality + clean-up is a love story, always make them a pair right away”. Or today, if you want robust code, learn Rust. That one’s centered around the worst mistakes of C and the likes.
C trains you. It forces you to think about what the code actually does because it doesn’t hold your hand like some kind of toddler. Java, Python, C# and even C++ programmers like to think there’s no trade off with encapsulating string operations into a class that handles memory access as an implementation detail. And their programs run slow as shit because they never see how heap allocation is killing performance.
I started learning minor coding syntax at the beginning of this year and over time ended up branching out into broader topics throughout computer science. As i traveled down the self taught rabbit hole of software engineering that im still currently traversing I began to realize that, just like any topic or niche topic that exists on the internet, there is a complex online community with its own unique culture around the topic of software engineering and the ways one might go about educating themselves within this field. I feel like clicking this article and being able to laugh pretty quickly at this relatively obscue human marks a pretty significant milestone in my personal journey. Does anyone else get a similar feeling from this or another similar type of media or possibly remember a similar experience when exploring this topic with which you can relate?
It’s not that hard! Yes, C has it’s quirks like any language, maybe even more of them. Since C has been around for nearly half a century, it’s going to have some missing features and safe strings are one of those. But anything C99 or newer has these problems solved. If you really want to code in a language that is more than 20 years old, you will have to do some of the heavy lifting.
My first guess is you are a millennial. My second guess is you have a degree in computer science, of which you are overly proud. Glad folks like you were nowhere to be found when we were bootstrapping programming with hardware switches and assembly language. What makes C great is that its like a bicycle WITHOUT the G.D. training wheels.
And they go immediately for the trivial fence post error. I started learning C/C++ 19 years ago and my first book on C already told me not to do this. At this point, you’re not even trying to make a valid point in favor of this dumb “let’s ban pointer arithmetic because actually thinking about what my code does behind the scenes is hard” fad that every new programming language has to religiously adhere to.
If you don’t understand what the problems with this code are: The code does not check if the user input would fit in the string’s set length or that it is a valid input, meaning a user could easily put whatever they want in and overflow the 3-character-long buffer defined in the “buff” variable. Since C requires you to manage memory yourself, it won’t change the buffer size to accomadate any larger data, leading to stuff beyond the string’s memory location being overwritten, which is of course not good. Another problem is that this code doesn’t account for the null terminator, which is what closes off a string of characters, so technically that buffer would overflow if given 3 characters regardless.
My solution: read user input one character at a time, and copy each character in an array. Once you reach one byte short of the end of the array, finish reading the user input, but simply don’t copy any more of it in the array, and always add a ‘\\0’ after the reading loop. If you don’t finish reading stdin, whatever is left in the buffer will be fed into your program at the next input that’s required from the user. In my experience, even using fflush(stdin) wouldn’t prevent the extra data to mess the following inputs, so it really is the safer bet.
The reason why the program is unsafe is because you’re also going to copy a null byte at the end, meaning buff would need to be 4 bytes long and not 3. Also you don’t need to copy to a buffer, I think it might be easier to just do a strcmp between argv and “DOG” or “CAT” and do the respective stuff for each case. It might also be safer because you can start easily overflowing the buffer even if the size was 4 characters long by just typing in more characters and you might be able to make the thing run bad code making the program have a security flaw as well. Edit: you’re welcome I guess..
This gives me flashbacks to a C++ assignment where we were required to use some weird archaic form of C strings to buffer text from a file. How the hell am I supposed to fix segfaults in code I didn’t write? Ever think of that, Intellisense? That was the only assignment in that class I didn’t clutch up and get working at the last possible second. I have no clue what was wrong with it other than cursed requirements. I’ve never had to deal with a segfault before or since. Next time I need to find a word in a file, I’ll just use grep (or Select-String, or vectors, or a normal freaking C++ string), thank you very much.
1) argc is not checked if argv has 2 arguments. 2) strcpy is unsafe to begin with (it doesn’t check the buffer’s length) use strcpy_s 3) buff is not properly zeroed which can cause issues if the string doesn’t contain a null terminator 4) in some rare cases argv can be NULL however it shouldn’t ever on the latest libc. It used to be like that in much much older versions 5) There is no return (technically not needed, still undefined behavior within C. Though pretty sure it was specified to be allowed JUST for main.) Following issues: SEGFAULT, STACKSMASHING, BUFFEROVERRUN. Did i miss anything?
If you are wondering (unlikely since everyone seems to be a C dev), argv is always the program. argv will be an argument, but if you just run “./program” or “program” argv isn’t there. You will get a segmentation fault. buff is also not long enough to store “cat” nor “dog” including a null terminator and checking the length of argv after checking it EXISTS would be ideal.
It didn’t specify that it reads a command line argument so is this sufficient? It will terminate if the buffer overflows but that’s what makes it secure. #include int main() { \tprintf(“Please input either \”CAT\” or \”DOG\”\ “); \tchar input; \tscanf(“%s”, &input); \tif (input == ‘C’ && input == ‘A’ && input == ‘T’) \t\tprintf(“meow\ “); \telse if (input == ‘D’ && input == ‘O’ && input == ‘G’) \t\tprintf(“woof\ “); \telse \t\tprintf(“That isn’t a valid string\ “); \treturn 0; }
you forgot to dereference the pointer pointing to a pointer referencing a pointer to allocated static memory of the size of 5 gigashits and you forgot to overload the operators ++ and =, so now you won’t be able to iterate through your strings, which actually should be stored in a binary file that you need to calculate yourself, and the file should be located on a hard drive on the dark side of the moon
So aside from the null terminator being left out, there is also the issue of bounds checking the number of arguments passed to the program. He never checked argc to make sure the minimum required number of arguments was present. Now, argc will be at least 1 (correct me if I’m wrong), but the first argument is always the name of the executable; since one more argument was required, he needed to make sure argc was at least 2.
I am studying computer science in Italy as an Italian and it makes me very sad when I come across situations like this. We are taught about the “input buffer”, but our teachers simply tell us to use “fflush” without providing any explanation on how we can create our own version of this function. This lack of guidance and support is disheartening
Hello, sptr = &S(i); 23 24 printf(“Enter name: “); 25 scanf(“%(^\ )s”,sptr->name); I am having issue here when I use selective scanf then none of this input buffer works..what approach should I use? My program is regarding students information using structure array and accessing through structure pointer
Your program is an example for several things. #1 The C stdlib is not designed well … this is a well known, and often discussed fact. #2 mixing fgets() with scanf() is usually a bad idea. better practise is to use fgets() to read a line from stdin, then parse this line using sscanf() #3 Do not forget to check returncodes from functions.
thank you. when i was 18y.o. i had left the institute after they had given us Turbo Pascal 5.0 instead of C. now i am 43y.o. and i was doing K&R exersises and my code was behaving badly after i’d chained several inputs. p.s. oh by the way —about C —while local wikipedians rant that the language is obsolete nowadays, i wanna to share some specifics (weirdness) of physical being’s implementation —i do not feel pain (anandamide is not destroyed) m.youtube.com/watch?v=4nGFNayjYrM thank you