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Format String Vulnerabilities in Cryptography and Network Security

Format String Vulnerability problem was first found in C language. The problem refers to a bug found in the printf function. The printf function is widely used for the transmission of ASCII data to the standard output. When we use the printf function properly then the text string becomes an automated conversion type. 

When the data stored in the printf function is executed by software, the format string attacks the surface of data at that time. When this attack happens, then the attacker easily inserts some malicious code in the input string, and that malicious code causes the temporary software execution failure. Depending upon the attack on the system, it can lead the abnormal system behavior. The most common family members of printf affected by these threats are vsprintf, vfprintf, fprintf, vsnprintf, and sprint.

This threat was first spotted by Tymm Twillman in September 1999. This threat was first attacked by the C language-based server, ProFTpd. During this threat, he spotted a printf function that caused the transmission of user-created data into the server. For better understanding, Tymm Twillman goes through many testing available print functions. He concluded from all the tests that string-related loopholes perform multiple threads. Using this loophole, the attacker can cause malfunctioning at the root of the system. 

Damaged Caused by the Attackers

If we overlook the attacks for a long time then cyber attackers can cause many problems. These problems are as follows:

  1. For the longest time of cyberattack, it causes unexpected crashing of code.
  2. Unauthorized access to our essential data.
  3. Execution of arbitrary code in our application.
  4. Successful Denied of service.

Format String Vulnerabilities in C Programs

We can perform several types of arguments in C language using the printf function. The program becomes very vulnerable when the unwanted outputs are inserted by the attackers. 

In C programs, format stringing is the most common. Without a specifier, it can cause so much trouble for the attackers. 

Let's understand this by a coding statement.


In the above statement, only the first stack is executed successfully and the rest of the stack specifier was conducted accordingly. 

Web applications

Some web applications containing the C language have the chance of attack by attackers. The possibility of this attack increases are high in web application maximum of web servers are created with the help of C or C++ languages. So, code vulnerability can be quickly done by attackers. In Javascript, the format string also causes trouble to the code. Also, PHP has the same code vulnerability problem because of the format string. 

Measures to Prevent Format String Attacks 

For safe and secure software development, no vulnerability should be ignored. Here are a few tips to follow for its early and certainly fixation:

  • Make sure that the string is not defined as an input type. It should always be described as a program part.
  • Try to use constant strings and do early extraction of variable parts.
  • Format_Guard.Rare is an excellent preventive tool that can fix all patches to glibc and protect against various format bugs. Use it at the designing stage. 
  • Promote regular use of the printf function. As long as it's used correctly, no vulnerability will be able to create havoc. 
  • Use Kimchi, which is a famous binary rewriting solution. It's designed to prevent the occurrence of string format loopholes during the runtime. It monitors the machine code calls that printf receives and replaces them with the safest possible version of printf, safe_printf.
  • Create dynamic addresses using ASLR or Address Space Layout Randomization. It's helpful to create dynamic lessons for functions, libraries, variables, and other crucial aspects. Dynamic addresses are not easy to manipulate. Hence, the odds of string-related attacks are low. 
  • Never ignoring compiler warnings is also a great format string attack prevention technique to try on. During the development, compilers notify the developers of the presence of vulnerable functions. A responsible developer takes this warning seriously and replaces the weak part immediately with a safe version. 

Note: For C language, the function string is the essential part, and for other programming languages, the vulnerability of code performs a massive error in the program.