Buffer Overflow; Avoiding overflow attacks

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I'm looking at this code example for class and I am new with buffer overflows. How can this exmple be modified to avoid buffer overflow attacks? Also, If anyone knows of a good article on buffer overflows, please post it. Thanks!

void GetProfileFor( const char *name,
              char *profile,
              int profileLen );

int main() {
              char *profile = malloc( 1024 );
              char name[128];

              printf( "Enter your name: " );
              gets( name );

              GetProfileFor( name, profile, 1024 );
              printf( "\nYour profile: %s\n", profile );
return 0; }

To identify where buffer overflow will occur you will have to identify all the input path and the buffer it filled up - is the internal buffer sufficient to cater for all poissible input? Or is there any limits imposed on the amount of inputs allowed?

In your case the gets(name) has a limit in internal buffer, but gets() itself has no limits in the input it can take:

http://www.tutorialspoint.com/c_standard_library/c_function_gets.htm

therefore buffer overflow is possible.

The specific solution to prevent this attack is to use fgets():

http://www.tutorialspoint.com/c_standard_library/c_function_fgets.htm

which does have a limit placed on the external inputs allowed.

What is a Buffer Overflow, How to Prevent Buffer Overflows. Developers can protect against buffer overflow vulnerabilities via security measures in their code, or by using languages that offer� What is Buffer Overflow. Buffers are memory storage regions that temporarily hold data while it is being transferred from one location to another. A buffer overflow (or buffer overrun) occurs when the volume of data exceeds the storage capacity of the memory buffer. As a result, the program attempting to write the data to the buffer overwrites adjacent memory locations.

Looking at just the code you posted, I found one line of code that you can change.

Replace

gets(name);

with

fgets(name, 128, stdin);

gets does not check the size of name to decide when to stop reading. It will try to read more characters than name has space for. fgets, on the other hand, will stop reading when it encounters a newline or it has read 127 characters, whichever is first.

Checkout Why gets() is bad / Buffer Overflows for more details.

Prevent Buffer Overflow Attacks, Prevent buffer overflow attacks. Scan your application to find buffer overflow vulnerabilities and get results instantly. Start free today. A buffer overflow occurs when a program or process attempts to write more data to a fixed length block of memory, or buffer, than the buffer is allocated to hold.

The most new compilers are adding stack protectors eg. canaries to the binary. You can still overflow the buffer, but you cant jump to the stack and execute shellcode and etc. You could brute force the canary, but it would probably take a long time. Also when you look at the man page of gets, in the bug section it says never use fgets

How to prevent buffer overflow attacks - SearchSecurity, Read up on types of buffer overflow attacks, and learn secure coding best practices that prevent such vulnerabilities, as well as post-deployment steps to keep� Buffer overflow results from a well-known, easily understood programming error. If a program doesn't check for overflow on each character and stop accepting data when its buffer is filled, a

Buffer Overflow Vulnerabilities, Exploits & Attacks, To prevent buffer overflow, developers of C/C++ applications should avoid standard library functions that are not bounds-checked, such as gets, scanf and strcpy. A buffer overflow occurs when more data are written to a buffer than it can hold. The excess data is written to the adjacent memory, overwriting the contents of that location and causing unpredictable results in a program. Buffer overflows happen when there is improper validation (no bounds prior to the data being written. It is considered a bug or weakness in the software.

Buffer Overflow, Buffer Overflow. Description of Buffer Overflow. See the OWASP article on Buffer Overflow Attacks. How to Avoid Buffer Overflow Vulnerabilities. See the� A buffer overflow or overrun is a memory safety issue where a program does not properly check the boundaries of an allocated fixed-length memory buffer and writes more data than it can hold. This

How to Detect, Prevent, and Mitigate Buffer Overflow Attacks, A security expert discusses buffer overflows, giving some past examples such as Heartbleed, provides examples of vulnerable code, and how� A buffer overflow is a situation where a running program attempts to write data outside the memory buffer which is not intended to store this data. When this happens we are talking about a buffer overflow or buffer overrun situation. A memory buffer is an area in the computer’s memory (RAM) meant for temporarily storing data.

Comments
  • Some robustness can be added, fgets(name, sizeof name, stdin). Then a buffer overflow can't be caused by later deciding to make the buffer smaller.