Dip Your Toes in the Sea of Security (PHP South Africa 2017)

@asgrim
Dip Your Toes in
the Sea of Security
James Titcumb
PHP South Africa 2017

$ whoami
James Titcumb
www.jamestitcumb.com
www.roave.com
@asgrim

@asgrim
Some simple PHP code...
<?php
$a = (int)filter_var($_GET['a'],
FILTER_SANITIZE_NUMBER_INT);
$b = (int)filter_var($_GET['b'],
FILTER_SANITIZE_NUMBER_INT);
$result = $a + $b;
printf('The answer is %d', $result);

@asgrim
The Golden Rules
(my made up golden rules)

@asgrim
4. Don’t reinvent the wheel

@asgrim
5. Never trust anything

@asgrim
OWASP
& the OWASP Top 10
https://www.owasp.org/

@asgrim
Application Security
(mainly PHP applications)

@asgrim
Always remember…
Filter Input
Escape Output

@asgrim
© 2003 Disney/Pixar. All Rights Reserved.
SQL Injection (#1)

@asgrim
SQL Injection (#1)
http://xkcd.com/327/

@asgrim
SQL Injection (#1)
<?php
// user_id=1; DROP TABLE users; --
$user_id = $_GET['user_id'];
$sql = "
SELECT * FROM users
WHERE user_id = {$user_id}";
$db->execute($sql);
✘

@asgrim
SQL Injection (#1)
<?php
$user_id = $_GET['user_id'];
$sql = "
SELECT * FROM users
WHERE user_id = :userid";
$stmt = $db->prepare($sql);
$stmt->bind('userid', $user_id);
$stmt->execute();
✓

@asgrim

@asgrim
exec($_GET)
https://github.com/search?q=exec%28%24_GET&ref=cmdform&type=Code

@asgrim
eval()
https://github.com/search?q=eval%28%24_GET&type=Code&ref=searchresults

@asgrim
Cross-Site Scripting / XSS (#3)

@asgrim
Cross-Site Scripting / XSS (#3)
<?php
$unfilteredInput = '<script type="text/javascript">...</script>';
// Unescaped - JS will run :'(
echo $unfilteredInput;
// Escaped - JS will not run :)
echo htmlspecialchars($string, ENT_QUOTES, 'UTF-8');

@asgrim
Cross-Site Request
Forgery / CSRF (#8)
http://www.factzoo.com/invertebrates/cuttlefish-chameleon-of-the-sea.html

@asgrim
Cross-Site Request Forgery / CSRF (#8)
<?php
if (!$isPost) {
$csrfToken = base64_encode(random_bytes(32)));
$_SESSION['csrf_token'] = $csrfToken;
// ... output the form ...
echo '<input type="hidden" name="csrf_token" value="'.$csrfToken.'" />';
} else if ($isPost) {
if (hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'])) {
die("Token invalid...");
}
// ... handle the form ...
}

@asgrim
<?php
if (!$isPost) {
$csrfToken = base64_encode(random_bytes(32)));
$_SESSION['csrf_token'] = $csrfToken;
// ... output the form ...
echo '<input type="hidden" name="csrf_token" value="'.$csrfToken.'" />';
} else if ($isPost) {
if (hash_equals($_SESSION['csrf_token'], $_POST['csrf_token'])) {
die("Token invalid...");
}
// ... handle the form ...
}
Cross-Site Request Forgery / CSRF (#8)

@asgrim
Timing attacks
// From zend_is_identical:
return (Z_STR_P(op1) == Z_STR_P(op2) ||
(Z_STRLEN_P(op1) == Z_STRLEN_P(op2) &&
memcmp(Z_STRVAL_P(op1), Z_STRVAL_P(op2), Z_STRLEN_P(op1)) == 0));

@asgrim
Timing attacks
Actual string: “foobar”
● a (0.00001)
● aa (0.00001)
● aaa (0.00001)
● aaaa (0.00001)
● aaaaa (0.00001)
● aaaaaa (0.00002) ← success!
● aaaaaaa (0.00001)
● aaaaaaaa (0.00001)
● aaaaaaaaa (0.00001)

@asgrim
Timing attacks
1 int memcmp(const void* s1, const void* s2,size_t n)
2 {
3 const unsigned char *p1 = s1, *p2 = s2;
4 while(n--)
5 if( *p1 != *p2 )
6 return *p1 - *p2;
7 else
8 p1++,p2++;
9 return 0;
10 }
http://clc-wiki.net/wiki/C_standard_library:string.h:memcmp#Implementation

@asgrim
Timing attacks
Actual string: “foobar”
● “aaaaaa” (0.00001)
● “baaaaa” (0.00001)
● …
● “faaaaa” (0.00002) ← success!
● “fbaaaa” (0.00002)
● “fcaaaa” (0.00002)
● …
● “foaaaa” (0.00003) ← success!

@asgrim
Sensitive Data Exposure (#6)

@asgrim
curl + https
<?php
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, false);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
✘

@asgrim
curl + https
<?php
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 2);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, true);
curl_setopt($ch, CURLOPT_CAINFO, "/path/to/certificate");
✓

@asgrim
Third Party Code
!!! WARNING !!!

@asgrim
Third Party Code
github.com/ /SecurityAdvisories
!!! WARNING !!!

@asgrim
Dependencies Disappearing

@asgrim
We are not all
security experts!

@asgrim
We are not all
security experts!
… but we CAN write secure code

@asgrim
Hack your own system!

@asgrim
What do you want?
Think like a hacker

@asgrim
How do you get it?
Think Differently

@asgrim
Threat Modelling
D.R.E.A.D.
© Buena Vista Pictures

@asgrim
Threat Modelling
Damage
R
E
A
D

@asgrim
Threat Modelling
Damage
Reproducibility
E
A
D

@asgrim
Threat Modelling
Damage
Reproducibility
Exploitability
A
D

@asgrim
Threat Modelling
Damage
Reproducibility
Exploitability
Affected users
D

@asgrim
Threat Modelling
Damage
Reproducibility
Exploitability
Affected users
Discoverability

@asgrim
Rank them in order
And fix them!

@asgrim
Authentication
& Authorization

@asgrim
Authentication
Verifying Identity

@asgrim
Case Study: Custom Authentication
We thought about doing this…

@asgrim
Case Study: Custom Authentication
We thought about doing this…
✘

@asgrim
Password Hashing
password_hash()
(basically, bcrypt with proper salt)

@asgrim
Two Factor Authentication

@asgrim
Authorization
Verifying Access

@asgrim
CRYPTOGRAPHY
IS
HARD
NEVER EVER “ROLL YOUR OWN”

@asgrim
CRYPTOGRAPHY
IS
HARD
NEVER EVER “ROLL YOUR OWN”
EVER!!!

@asgrim
I’ve got some
great ideas for
encryption...
Image: IBTimes (http://goo.gl/zPVeo0)

@asgrim
How to encrypt then?
sodium+halite or Defuse php-encryption

@asgrim
Create an SSH Fortress

@asgrim
iptables
#!/bin/bash
IPT="/sbin/iptables"
$IPT --flush
$IPT --delete-chain
$IPT -P INPUT DROP
$IPT -P FORWARD DROP
$IPT -P OUTPUT DROP
# Loopback
$IPT -A INPUT -i lo -j ACCEPT
$IPT -A OUTPUT -o lo -j ACCEPT
# Inbound traffic
$IPT -A INPUT -p tcp --dport ssh -j ACCEPT
$IPT -A INPUT -p tcp --dport 80 -j ACCEPT
$IPT -A INPUT -p tcp --dport 443 -j ACCEPT
# Outbound traffic
$IPT -A OUTPUT -p tcp --dport 80 -j ACCEPT
$IPT -A OUTPUT -p tcp --dport 443 -j ACCEPT
$IPT -A OUTPUT -p udp --dport 53 -m state --state NEW -j ACCEPT

@asgrim
iptables
https://twitter.com/sadserver/status/615988393198026752

@asgrim
ufw
sudo ufw enable
sudo ufw allow 22
sudo ufw allow 80

@asgrim
Mitigate Brute Force Attacks

@asgrim
Install Only What You Need

@asgrim
Case Study: Be Minimal
Internets
Postfix
Squid Proxy
(badly configured)
hacker
spam

@asgrim
Resources
● http://securingphp.com/
● https://www.owasp.org/
● http://blog.ircmaxell.com/
● https://github.com/paragonie/random_compat
● https://github.com/paragonie/sodium_compat
● https://github.com/ircmaxell/password_compat
● https://paragonie.com/blog
● https://websec.io/resources.php
● https://www.digitalocean.com/community/tutorials/initial-server-setup-with-ubuntu-16-04
● https://www.kali.org/

@asgrim
The Golden Rules
1. Keep it simple
2. Know the risks
3. Fail securely
4. Don’t reinvent the wheel
5. Never trust anything / anyone

@asgrim
If you follow all this, you get...

Any questions?
Please leave feedback!
https://joind.in/talk/b8bd0
James Titcumb
@asgrim

Dip Your Toes in the Sea of Security (PHP South Africa 2017)

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