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Improper input validation [1] or unchecked user input is a type of vulnerability in computer software that may be used for security exploits. [2] This vulnerability is caused when "[t]he product does not validate or incorrectly validates input that can affect the control flow or data flow of a program." [1] Examples include: Buffer overflow
What the user may consider as valid input may contain token characters or strings that have been reserved by the developer to have special meaning (such as the ampersand or quotation marks). The user may submit a malformed file as input that is handled properly in one application but is toxic to the receiving system.
In PHP, HTML sanitization can be performed using the strip_tags() function at the risk of removing all textual content following an unclosed less-than symbol or angle bracket. [2] The HTML Purifier library is another popular option for PHP applications. [3] In Java (and .NET), sanitization can be achieved by using the OWASP Java HTML Sanitizer ...
The function was supposed to sanitize its argument, which came from user input and then pass the input to the Unix shell, to be run in the security context of the Web server. The script did not correctly sanitize all input and allowed new lines to be passed to the shell, which effectively allowed multiple commands to be run.
The function will result in undefined behavior when the input is over 1000 characters. Some programmers may not feel that this is a problem, supposing that no user will enter such a long input. This particular bug demonstrates a vulnerability which enables buffer overflow exploits. Here is a solution to this example:
The target PHP file then accesses the data passed by the form through PHP's $_POST or $_GET variables, depending on the value of the method attribute used in the form. Here is a basic form handler PHP script that will display the contents of the first_name input field on the page: form.html
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A code sanitizer is a programming tool that detects bugs in the form of undefined or suspicious behavior by a compiler inserting instrumentation code at runtime. The class of tools was first introduced by Google's AddressSanitizer (or ASan) of 2012, which uses directly mapped shadow memory to detect memory corruption such as buffer overflows or accesses to a dangling pointer (use-after-free).