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Web Application Penetration Testing
$ curl -kis http:/example.com/restricted/
HTTP/1.1 401 Authorization Required
Date: Fri, 01 Aug 2013 00:00:00 GMT
WWW-Authenticate: Basic realm=”Restricted Area”
Accept-Ranges: bytes
Vary: Accept-Encoding
Content-Length: 162
Content-Type: text/html
401 Authorization Required
401 Authorization Required
Invalid login credentials!
Testing for Weak SSL/TLS Ciphers/Protocols/Keys vulnerabilities
The large number of available cipher suites and quick progress
in cryptanalysis makes testing an SSL server a non-trivial task.
At the time of writing these criteria are widely recognized as
minimum checklist:
• Weak ciphers must not be used (e.g. less than 128 bits [10]; no
NULL ciphers suite, due to no encryption used; no Anonymous
Diffie-Hellmann, due to not provides authentication).
• Weak protocols must be disabled (e.g. SSLv2 must be disabled,
due to known weaknesses in protocol design [11]).
• Renegotiation must be properly configured (e.g. Insecure
Renegotiation must be disabled, due to MiTM attacks [12] and
Client-initiated Renegotiation must be disabled, due to Denial of
Service vulnerability [13]).
• No Export (EXP) level cipher suites, due to can be easly broken
[10].
• X.509 certificates key length must be strong (e.g. if RSA or DSA
is used the key must be at least 1024 bits).
• X.509 certificates must be signed only with secure hashing
algoritms (e.g. not signed using MD5 hash, due to known collision
attacks on this hash).
• Keys must be generated with proper entropy (e.g, Weak Key
Generated with Debian) [14].
A more complete checklist includes:
• Secure Renegotiation should be enabled.
• MD5 should not be used, due to known collision attacks. [35]
• RC4 should not be used, due to crypto-analytical attacks [15].
• Server should be protected from BEAST Attack [16].
• Server should be protected from CRIME attack, TLS compres
sion must be disabled [17].
• Server should support Forward Secrecy [18].
The following standards can be used as reference while assessing
SSL servers:
• PCI-DSS v2.0 in point 4.1 requires compliant parties to use
“strong cryptography” without precisely defining key lengths and
algorithms. Common interpretation, partially based on previous
versions of the standard, is that at least 128 bit key cipher, no
export strength algorithms and no SSLv2 should be used [19].
• Qualys SSL Labs Server Rating Guide [14], Depoloyment best
practice [10] and SSL Threat Model [20] has been proposed to
standardize SSL server assessment and configuration. But is less
updated than the SSL Server tool [21].
• OWASP has a lot of resources about SSL/TLS Security [22],
[23], [24], [25]. [26].
Some tools and scanners both free (e.g. SSLAudit [28] or SSLScan
[29]) and commercial (e.g. Tenable Nessus [27]), can be used to assess
SSL/TLS vulnerabilities. But due to evolution of these vulnerabilities
a good way to test is to check them manually with openssl
[30] or use the tool’s output as an input for manual evaluation using
the references.
Sometimes the SSL/TLS enabled service is not directly accessible
and the tester can access it only via a HTTP proxy using CONNECT
method [36]. Most of the tools will try to connect to desired tcp port
to start SSL/TLS handshake. This will not work since desired port is
accessible only via HTTP proxy. The tester can easily circumvent this
by using relaying software such as socat [37].
Example 2. SSL service recognition via nmap
The first step is to identify ports which have SSL/TLS wrapped services.
Typically tcp ports with SSL for web and mail services are -
but not limited to - 443 (https), 465 (ssmtp), 585 (imap4-ssl), 993
(imaps), 995 (ssl-pop).
In this example we search for SSL services using nmap with “-sV”
option, used to identify services and it is also able to identify SSL
services [31]. Other options are for this particular example and must
be customized. Often in a Web Application Penetration Test scope is
limited to port 80 and 443.
$ nmap -sV --reason -PN -n --top-ports 100 www.example.
com
Starting Nmap 6.25 ( http:/nmap.org ) at 2013-01-01 00:00
CEST
Nmap scan report for www.example.com (127.0.0.1)
Host is up, received user-set (0.20s latency).
Not shown: 89 filtered ports
Reason: 89 no-responses
PORT STATE SERVICE REASON VERSION
21/tcp open ftp syn-ack Pure-FTPd
22/tcp open ssh syn-ack OpenSSH 5.3 (protocol 2.0)
25/tcp open smtp syn-ack Exim smtpd 4.80
26/tcp open smtp syn-ack Exim smtpd 4.80
80/tcp open http syn-ack
110/tcp open pop3 syn-ack Dovecot pop3d
143/tcp open imap syn-ack Dovecot imapd
443/tcp open ssl/http syn-ack Apache
465/tcp open ssl/smtp syn-ack Exim smtpd 4.80
993/tcp open ssl/imap syn-ack Dovecot imapd
995/tcp open ssl/pop3 syn-ack Dovecot pop3d
Service Info: Hosts: example.com
Service detection performed. Please report any incorrect results
at http:/nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 131.38 seconds