PHP Developers Network

I am updating myself on PHP security issues for the last 2 days.
Here is a gist of things that I have collected from various sources to do as a part of my security regimen:

1. Use $_POST variable instead of $_REQUEST
2. Check all user inputs with regex (even the drop-down boxes, radio buttons, checkboxes to avoid form spoofing)
3. mysql_real_escape_string() to avoid SQL injections
4. htmlentities() - to avoid XSS attacks
5. keep url parameter different from actual field names in database
6. rewrite url to clean url (to hide parameters)
7. remove .php extension with .htacess
8. session token to prevent session hijacking
9. error_reporting turned off in a production site
10 register_globals disabled on production site
11 Initialize all variables in scripts
12 Avoid specifying dynamic paths in include, require etc like include ('$path/abc.php');
13 put single quotes around all values in your SQL statements

I have not mentioned password encrypting in the list because am yet to update myself after the MD5 debacle.
I know this can be a never ending topic but anything vital that i am missing ?

1. Use $_POST or $_GET. The reason for avoiding $_REQUEST is that POST/GET variables can overwrite depending on the configuration settings.

3. Don't use the mysql extension. Use mysqli or PDO instead.

5-7. Not sure these are real security measures, but can't hurt.

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2. Regex is expensive. Check that there isn't already a function that does what you need; often overlooked functions are for positive integers, for alphanumerics, and for numbers.
4. htmlentities() for HTML, htmlspecialchars() for XML.
5. Use what's sensible.
6. Not really a security thing.
7. Doesn't matter.
10. And development servers too. Dev should be as close to prod as possible.
12. You can if you're very careful about it.
13. Not really a security thing: you have to quote strings. Single or double? Doesn't matter if you're escaping the values properly.

Also
- Whitelists (using known good values) are better than blacklists (not using known bad values)
- CSRF tokens on important forms (wouldn't hurt for all forms too)
- Upload directories (a) outside the web root and/or (b) carefully protected against file execution and/or (c) inaccessible except through a "download" script
- Other stuff that I'm not thinking of

I indeed have a user table with username field.

Thanks for your clarifications. All points taken

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There are 10 types of people in this world, those who understand binary and those who don't

scuse me,
1.I don't really understand the XSS attack part. htmlentities() is useful only when you're trying to render HTML input to client's browser, correct? so when data flows out from the server into client? Suppose I never manipulate browser's DOM (because all server response are in text form), is it safe to say that my web app is immune to XSS attack?
2. as for SQL injection and mysql_real_escape_string(), I thought escaping and wrapping the input string from user input is enough? I just do 4 things to achieve this objective :

that's all
3. for session related, I just perform session regeneration, set session timeout and disable the url containing session (forgot the name). so always use cookies.

With these, does my app still have vulnerabilities? thanks

the text here means the server only returns AJAX text response to be parsed into JSON, so no renderring. Other type of server's text response is URL that will be executed using Header location..

as for mysql_real_escape_string(), do you mean this one function accompanied with prepared statement is the silver bullet to thwart all kinds of SQL Injection? that's great news. Will that work to all database vendors (oracle, sql server, postgre, etc)? because I always thought, as the name implies, only works for mysql

you also said about the session regeneration that it's still possible to hijack the session? if so, could you elaborate a little bit? a little code would be appreciated. Thanks

Okay, so PHP isn't doing any rendering. So the next question is whether your JavaScript does. If so then you're potentially vulnerable (depending how you do the rendering).

As you saw, mysql_real_escape_string() is for MySQL only, but most of the other vendors have a similar function. Prepared statements are the alternative; arguably meant for a different purpose, you can use them to be 100% safe from SQL injection. Either you construct queries by hand and use mysql_real_escape_string() or you use prepared statements. One or the other but not both (for the same query, that is).

As for session regeneration, the malicious sniffer has at least two options:
1. Intercept a session ID and fire off a request before the original user can send their next one. This can allow for concurrent browsing if you aren't completely destroying old sessions and aren't ensuring one session per user.
2. Wait until the user has stopped browsing and resume where they left off.

for the sql injection part:

let's say I'm using mysql, so the code would be something like:



and the DB code 1:


or DB code 2, this one is without mysql_real_escape_string:


and that's it right? both DB code 1 and 2 are now 100% sql injection free, even when db code 2 does not call sanitizeInput at all. CMIIW. thanks

what about DB code 2? is it free of SQL injection? even without calling sanitizeInput at all?
also, I put critical files outside web root, is there any way at all to access those critical files via browser? or is it safe already?