Keep user data secure by sanitizing all input and output, using nonces to verify requests, and whitelisting/blacklisting known safe data formats. Common attacks like XSS, CSRF and viruses can be prevented by escaping output, validating referrers, and using antivirus software. The document provides links to WordPress resources on data validation and security best practices.

1. So you’re writing code
for the masses, huh?
Are you being responsible and protecting them from
getting pwned?

2. Watch This.
http://wordpress.tv/2011/01/29/mark-jaquith-theme-plugin-security/

3. That guy pwned a plugin I
wrote live on stage at
WordCamp New York.
It changed my life.

4. Read This.
http://wp.tutsplus.com/tutorials/creative-coding/data-sanitization-and-validation-with-wordpress/

5. tl;dr
• Keep your dev environment clean
• Escape your data output
• Sanitize your data inputs
• Validate referrers
• Core functionality should always trump your super
awesome functionality

6. Keep Your Dev Environment Clean
Don’t think that just because you’re on a mac you’re
safe from viruses.
If you’re on a PC, you should assume you’re already
pwned.

7. Kaspersky Anti-Virus
• I use it.
• Dre uses it.
• Tony uses it.
• You should be using it.

8. Trust No One,
Trust Nothing

9. XSS: Cross-site Scripting
Cross-site scripting (XSS) is a type of computer security vulnerability
typically found in Web applications. XSS enables attackers to inject
client-side script into Web pages viewed by other users. A cross-site
scripting vulnerability may be used by attackers to bypass access
controls such as the same origin policy. Cross-site scripting carried
out on websites accounted for roughly 84% of all security
vulnerabilities documented by Symantec as of 2007.[1] Their effect may
range from a petty nuisance to a significant security risk, depending on
the sensitivity of the data handled by the vulnerable site and the
nature of any security mitigation implemented by the site's owner.
http://en.wikipedia.org/wiki/Cross-site_scripting

10. Escape All The Things On Output
http://codex.wordpress.org/Data_Validation#Output_Sanitation
• Bad data will be tamed
• esc_{context}
• esc_js - Escape single quotes, htmlspecialchar " < > &, and fix
line endings.
• esc_html - Escaping for HTML blocks.
• esc_attr - Escaping for HTML attributes.
• esc_sql - Escapes data for use in a MySQL query.
• esc_url - Checks and cleans a URL.
• esc_textarea - Escaping for textarea values.

11. Sanitize All The Things On Input
http://codex.wordpress.org/Data_Validation#Input_Validation
• sanitize_* and similar functions help for most things
• $_POST = array(‘e’=>‘<script src=‘http://pwnd.com/u.js’></script>’)
• BAD: update_post_meta($id, ‘e’, $_POST[‘e’])
• GOOD: update_post_meta($id, ‘e’, sanitize_email($_POST[‘e’]))
• Note: Might unintentionally change data and give unexpected results

12. Whitelisting Data
http://codex.wordpress.org/Data_Validation#Whitelist
• Whitelisting data - Only accept known data
• $_POST = array(
‘pwn’=>‘<script src=‘http://pwnd.com/u.js’></script>’,
‘e’=‘email@domain.com’
);
• BAD:
• foreach( $_POST as $key => $val ) :
update_post_meta($id, $key, $val);
endforeach;
• GOOD: update_post_meta($id, ‘e’, sanitize_email($_POST[‘e’]))

13. Blacklisting Data
http://codex.wordpress.org/Data_Validation#Blacklist
• Blacklisting data - Only accept data if it’s in the proper format
• $_POST = array(
‘e’=‘me@domain.’
);
• if( is_email($_POST[‘e’]) )
update_post_meta( $id, ‘e’, sanitize_email($_POST[‘e’]) );

14. CSRF: Cross-site Request Forgery
Cross-site request forgery, also known as a one-click attack or session
riding and abbreviated as CSRF (sometimes pronounced sea-surf[1]) or XSRF,
is a type of malicious exploit of a website whereby unauthorized commands
are transmitted from a user that the website trusts.[2] Unlike cross-site
scripting (XSS), which exploits the trust a user has for a particular site,
CSRF exploits the trust that a site has in a user's browser.
http://en.wikipedia.org/wiki/Cross-site_request_forgery

15. Sweet, this might lead to my
next big deal! ACCEPT!

16. zOMG WTF?!
http://mysite.com/wp-admin/post.php?post=307&action=trash

17. Nonces FTW!
(http://codex.wordpress.org/WordPress_Nonces)
• Before the Request
• wp_nonce_url
• wp_create_nonce
• wp_nonce_field
• Verify the Request
• wp_verify_nonce
• check_admin_referer

18. Is there an API for that?

19. Professional WordPress
Plugin Development
http://amzn.to/plugindevbook