Security Recap
Because security is such an important issue, we want to reiterate the main points of this chapter as well as add a few additional tips:
Filter input to be sure that all data you receive from remote sources is the data you expect. Remember, the stricter your filtering logic, the safer your application.
Escape output in a context-aware manner to be sure that your data isn’t misinterpreted by a remote system.
Always initialize your variables. This is especially important when the
register_globals
directive is enabled.Disable
register_globals
,magic_quotes_gpc
, andallow_url_fopen
. See http://www.php.net for details on these directives.Whenever you construct a filename, check the components with
basename()
andrealpath()
.Store includes outside of the document root. It is better to not name your included files with the .inc extension. Name them with a .php extension, or some other less obvious extension.
Always call
session_regenerate_id()
whenever a user’s privilege level changes.Whenever you construct a filename from a user-supplied component, check the components with
basename()
andrealpath()
.Don’t create a file and then change its permissions. Instead, set
umask()
so that the file is created with the correct permissions.Don’t use user-supplied data with
eval()
,preg_replace()
with the/e
option, or any of the system commands—exec()
,system()
,popen()
,passthru()
, and the backtick (`
) operator.
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