Using the php Function mb_eregi_Replace_Callback()

mb_eregi_replace() is an inbuilt function in PHP which allows you to perform case-insensitive regular expression search and replace with multibyte support. The mb_eregi_replace() function scans the string for matches to pattern, and if a match is found it will replace the string with the replacement. It will then return the resultant string on success, or FALSE on error.

The mb_eregi_replace_callback() function is similar to the mb_eregi_replace() except that it takes in a callback function instead of the replacement string. The callback function can be any function that accepts an array as its input and returns a string as its output. The callback function must be defined by the application, and should have a unique name so it does not pollute the global functions namespace.

An attacker can create remote code execution vulnerabilities by using this function with untrusted data and a callback function with a vulnerable PHP script. The Vigilance Vulnerability Alerts team rates this as a moderate risk.

The use of mb_eregi_replace_callback() is not recommended in production. It is slower and less secure than the equivalent mb_eregi_replace(). In general, we recommend using preg_replace() instead because it is much faster and more secure. It also avoids the need for backslash escapes in callback functions. It is also worth noting that the mb_eregi_replace_callback() does not automatically escape its arguments like the mb_eregi_replace() does. Therefore it should only be used in testing environments where the security of untrusted input can be guaranteed.