Validating string input c. Validating input.



Validating string input c

Validating string input c

Any input that comes into a program from an external source — such as a user typing at a keyboard or a network connection — can potentially be the source of security concerns and potentially disastrous bugs.

All input should be treated as potentially dangerous. All interesting software packages rely upon external input. Although information typed at a computer might be the most familiar, networks and external devices can also send data to a program. Generally, this data will be of a specific type: If the correct type and form of data is provided, the program might work fine. However, if programs are not carefully written, attackers can construct inputs that can cause malicious code to be executed.

If video does not work, try refreshing the page: Risk — How can it happen? Any data that can enter your program from an external source can be a potential source of problems. If external data is not checked to verify that it has the right type of information, the right amount of information, and the right structure of information, it can cause problems. Input validation errors can lead to buffer overflows if the data being provided is used as an index into an array.

Input that is used as the basis for a database search can be used as the basis for SQL injections, which use carefully constructed inputs to make relational databases reveal data inappropriately or even destroy data. A Norwegian woman mistyped her account number on an internet banking system. Instead of typing her digit account number, she accidentally typed an extra digit, for a total of 12 numbers. A simple dialog box informing her that she had typed two many digits would have gone a long way towards avoiding this expensive error.

This program stores the squares of the number from one to ten in array, and then asks the user to type a number. The square of that number will then be returned: The first comes with the use of cin to read an integer from the console.

If the user types a number, this will work just fine. However, if the user types something that is not a number, the program may not work correctly.

Floating point values might be truncated to integers 3. A robust program would catch this error, provide a clear and appropriate error message, and ask the person to re-type their input. The second problem occurs when the array is accessed. Even if the user provides an appropriate integer, the value may be out of the range of the array.

An array containing 10 elements can only be accessed by indices 0,1, Thus, the only values of which that will work correctly are 1,2, Any values outside of this range will lead to an attempt to access a value outside the range of the array. In other languages, this may lead to a buffer overflow that might be exploited by malicious software. How can I properly validate input? The basic rule is for input validation is to check that input data matches all of the constraints that it must meet to be used correctly in the given circumstance.

In many cases, this can be very difficult: Some of the checks that you might want to use include: Input data should be of the right type.

Names should generally be alphabetic, numbers numeric. Punctuation and other uncommon characters are particularly troubling, as they can often be used to form the basis of code-injection attacks.

Many programs will handle input data by assuming that all input is of string form, verifying that the string contains appropriate characters, and then converting the string into the desired data type. Verify that numbers are within a range of possible values: For example, the month of a person's date of birth should lie between 1 and Another common range check involves values that may lead to division by zero errors.

Check that values make sense: Guarantee presence of important data — the omission of important data can be seen as an input validation error. Input that is either too long or too short will not be legitimate. Phone numbers generally don't have 39 digits; Social Security Numbers have exactly 9 Format: Dates, credit card numbers, and other data types have limitations on the number of digits and any other characters used for separation. For example, dates are usually specified by 2 digits for the month, one or two for the day, and either two or four for the year.

Identification numbers such as bank accounts, often have check digits: The check digit is determined by a calculation based on the remaining digits — if the check digit does not match the results of the calculation,either the ID is bad or the check digit is bad. In either case, the number should be rejected as invalid. Use appropriate language tools: The safety of tools that read user input varies across programming languages and systems.

Alternative libraries specifically designed with security in mind are often more robust. The choice of programming languages can play a role in the potential severity of input validation vulnerabilities. Untyped languages such as Perl and Ruby do not have any such requirements — any variable can store any type of value. Of course, these languages do not eliminate validation problems — you may still run into trouble if you use a string to retrieve an item from an integer- indexed array.

Some languages provide additional help in the form of built-in procedures that can be used to remove potentially damaging characters from input strings.

A robust program will respond to invalid input in a manner that is appropriate, correct, and secure. For user input, this will often mean providing an informative error message and requesting re-entry of the data.

Invalid input from other sources — such as a network connection — may require alternate measures.

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Reading User Input with Getline in C++



Validating string input c

Any input that comes into a program from an external source — such as a user typing at a keyboard or a network connection — can potentially be the source of security concerns and potentially disastrous bugs.

All input should be treated as potentially dangerous. All interesting software packages rely upon external input. Although information typed at a computer might be the most familiar, networks and external devices can also send data to a program. Generally, this data will be of a specific type: If the correct type and form of data is provided, the program might work fine.

However, if programs are not carefully written, attackers can construct inputs that can cause malicious code to be executed. If video does not work, try refreshing the page: Risk — How can it happen? Any data that can enter your program from an external source can be a potential source of problems. If external data is not checked to verify that it has the right type of information, the right amount of information, and the right structure of information, it can cause problems.

Input validation errors can lead to buffer overflows if the data being provided is used as an index into an array. Input that is used as the basis for a database search can be used as the basis for SQL injections, which use carefully constructed inputs to make relational databases reveal data inappropriately or even destroy data. A Norwegian woman mistyped her account number on an internet banking system. Instead of typing her digit account number, she accidentally typed an extra digit, for a total of 12 numbers.

A simple dialog box informing her that she had typed two many digits would have gone a long way towards avoiding this expensive error. This program stores the squares of the number from one to ten in array, and then asks the user to type a number. The square of that number will then be returned: The first comes with the use of cin to read an integer from the console.

If the user types a number, this will work just fine. However, if the user types something that is not a number, the program may not work correctly. Floating point values might be truncated to integers 3. A robust program would catch this error, provide a clear and appropriate error message, and ask the person to re-type their input. The second problem occurs when the array is accessed. Even if the user provides an appropriate integer, the value may be out of the range of the array. An array containing 10 elements can only be accessed by indices 0,1, Thus, the only values of which that will work correctly are 1,2, Any values outside of this range will lead to an attempt to access a value outside the range of the array.

In other languages, this may lead to a buffer overflow that might be exploited by malicious software. How can I properly validate input? The basic rule is for input validation is to check that input data matches all of the constraints that it must meet to be used correctly in the given circumstance. In many cases, this can be very difficult: Some of the checks that you might want to use include: Input data should be of the right type.

Names should generally be alphabetic, numbers numeric. Punctuation and other uncommon characters are particularly troubling, as they can often be used to form the basis of code-injection attacks. Many programs will handle input data by assuming that all input is of string form, verifying that the string contains appropriate characters, and then converting the string into the desired data type.

Verify that numbers are within a range of possible values: For example, the month of a person's date of birth should lie between 1 and Another common range check involves values that may lead to division by zero errors. Check that values make sense: Guarantee presence of important data — the omission of important data can be seen as an input validation error. Input that is either too long or too short will not be legitimate.

Phone numbers generally don't have 39 digits; Social Security Numbers have exactly 9 Format: Dates, credit card numbers, and other data types have limitations on the number of digits and any other characters used for separation.

For example, dates are usually specified by 2 digits for the month, one or two for the day, and either two or four for the year. Identification numbers such as bank accounts, often have check digits: The check digit is determined by a calculation based on the remaining digits — if the check digit does not match the results of the calculation,either the ID is bad or the check digit is bad.

In either case, the number should be rejected as invalid. Use appropriate language tools: The safety of tools that read user input varies across programming languages and systems. Alternative libraries specifically designed with security in mind are often more robust. The choice of programming languages can play a role in the potential severity of input validation vulnerabilities.

Untyped languages such as Perl and Ruby do not have any such requirements — any variable can store any type of value. Of course, these languages do not eliminate validation problems — you may still run into trouble if you use a string to retrieve an item from an integer- indexed array. Some languages provide additional help in the form of built-in procedures that can be used to remove potentially damaging characters from input strings. A robust program will respond to invalid input in a manner that is appropriate, correct, and secure.

For user input, this will often mean providing an informative error message and requesting re-entry of the data. Invalid input from other sources — such as a network connection — may require alternate measures.

Validating string input c

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4 Comments

  1. This is very similar to how firewalls protect computer networks from attackers; it won't prevent all attacks, but it does make a program much more resistant. The second problem occurs when the array is accessed. Punctuation and other uncommon characters are particularly troubling, as they can often be used to form the basis of code-injection attacks.

  2. Of course, these languages do not eliminate validation problems — you may still run into trouble if you use a string to retrieve an item from an integer- indexed array. As I'll discuss later, it's important to remember that users can reset cookie values and form data to anything they want.

  3. The choice of programming languages can play a role in the potential severity of input validation vulnerabilities.

  4. Otherwise, a possibly cracked related site might be able to insert spoofed cookies. Alternative libraries specifically designed with security in mind are often more robust.

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