1BO4r2U

Recommendations

Info

157 158 Web Application Penetration Testing Web Application Penetration Testing a weak cipher - or at worst no encryption - permitting to an attacker to gain access to the supposed secure communication channel. Other misconfiguration can be used for a Denial of Service attack. Common Issues A vulnerability occurs if the HTTP protocol is used to transmit sensitive information [2] (e.g. credentials transmitted over HTTP [3]). When the SSL/TLS service is present it is good but it increments the attack surface and the following vulnerabilities exist: • SSL/TLS protocols, ciphers, keys and renegotiation must be properly configured. • Certificate validity must be ensured. Other vulnerabilities linked to this are: • Software exposed must be updated due to possibility of known vulnerabilities [4]. • Usage of Secure flag for Session Cookies [5]. • Usage of HTTP Strict Transport Security (HSTS) [6]. • The presence of HTTP and HTTPS both, which can be used to intercept traffic [7], [8]. • The presence of mixed HTTPS and HTTP content in the same page, which can be used to Leak information. Sensitive data transmitted in clear-text The application should not transmit sensitive information via unencrypted channels. Typically it is possible to find basic authentication over HTTP, input password or session cookie sent via HTTP and, in general, other information considered by regulations, laws or organization policy. Weak SSL/TLS Ciphers/Protocols/Keys Historically, there have been limitations set in place by the U.S. government to allow cryptosystems to be exported only for key sizes of at most 40 bits, a key length which could be broken and would allow the decryption of communications. Since then cryptographic export regulations have been relaxed the maximum key size is 128 bits. It is important to check the SSL configuration being used to avoid putting in place cryptographic support which could be easily defeated. To reach this goal SSL-based services should not offer the possibility to choose weak cipher suite. A cipher suite is specified by an encryption protocol (e.g. DES, RC4, AES), the encryption key length (e.g. 40, 56, or 128 bits), and a hash algorithm (e.g. SHA, MD5) used for integrity checking. Briefly, the key points for the cipher suite determination are the following: [1] The client sends to the server a ClientHello message specifying, among other information, the protocol and the cipher suites that it is able to handle. Note that a client is usually a web browser (most popular SSL client nowadays), but not necessarily, since it can be any SSL-enabled application; the same holds for the server, which needs not to be a web server, though this is the most common case [9]. [2] The server responds with a ServerHello message, containing the chosen protocol and cipher suite that will be used for that session (in general the server selects the strongest protocol and cipher suite supported by both the client and server). It is possible (for example, by means of configuration directives) to specify which cipher suites the server will honor. In this way you may control whether or not conversations with clients will support 40-bit encryption only. [1] The server sends its Certificate message and, if client authentication is required, also sends a CertificateRequest message to the client. [2] The server sends a ServerHelloDone message and waits for a client response. [3] Upon receipt of the ServerHelloDone message, the client verifies the validity of the server’s digital certificate. SSL certificate validity – client and server When accessing a web application via the HTTPS protocol, a secure channel is established between the client and the server. The identity of one (the server) or both parties (client and server) is then established by means of digital certificates. So, once the cipher suite is determined, the “SSL Handshake” continues with the exchange of the certificates: [1] The server sends its Certificate message and, if client authentication is required, also sends a CertificateRequest message to the client. [2] The server sends a ServerHelloDone message and waits for a client response. [3] Upon receipt of the ServerHelloDone message, the client verifies the validity of the server’s digital certificate. In order for the communication to be set up, a number of checks on the certificates must be passed. While discussing SSL and certificate based authentication is beyond the scope of this guide, this section will focus on the main criteria involved in ascertaining certificate validity: • Checking if the Certificate Authority (CA) is a known one (meaning one considered trusted); • Checking that the certificate is currently valid; • Checking that the name of the site and the name reported in the certificate match. Let’s examine each check more in detail. • Each browser comes with a pre-loaded list of trusted CAs, against which the certificate signing CA is compared (this list can be customized and expanded at will). During the initial negotiations with an HTTPS server, if the server certificate relates to a CA unknown to the browser, a warning is usually raised. This happens most often because a web application relies on a certificate signed by a self-established CA. Whether this is to be considered a concern depends on several factors. For example, this may be fine for an Intranet environment (think of corporate web email being provided via HTTPS; here, obviously all users recognize the internal CA as a trusted CA). When a service is provided to the general public via the Internet, however (i.e. when it is important to positively verify the identity of the server we are talking to), it is usually imperative to rely on a trusted CA, one which is recognized by all the user base (and here we stop with our considerations; we won’t delve deeper in the implications of the trust model being used by digital certificates). • Certificates have an associated period of validity, therefore they may expire. Again, we are warned by the browser about this. A public service needs a temporally valid certificate; otherwise, it means we are talking with a server whose certificate was issued by someone we trust, but has expired without being renewed. • What if the name on the certificate and the name of the server do not match? If this happens, it might sound suspicious. For a number of reasons, this is not so rare to see. A system may host a number of name-based virtual hosts, which share the same IP address and are identified by means of the HTTP 1.1 Host: header information. In this case, since the SSL handshake checks the server certificate before the HTTP request is processed, it is not possible to assign different certificates to each virtual server. Therefore, if the name of the site and the name reported in the certificate do not match, we have a condition which is typically signaled by the browser. To avoid this, IP-based virtual servers must be used. [33] and [34] describe techniques to deal with this problem and allow name-based virtual hosts to be correctly referenced. Other vulnerabilities The presence of a new service, listening in a separate tcp port may introduce vulnerabilities such as infrastructure vulnerabilities if the software is not up to date [4]. Furthermore, for the correct protection of data during transmission the Session Cookie must use the Secure flag [5] and some directives should be sent to the browser to accept only secure traffic (e.g. HSTS [6], CSP). Also there are some attacks that can be used to intercept traffic if the web server exposes the application on both HTTP and HTTPS [6], [7] or in case of mixed HTTP and HTTPS resources in the same page. How to Test Testing for sensitive data transmitted in clear-text Various types of information which must be protected can be also transmitted in clear text. It is possible to check if this information is transmitted over HTTP instead of HTTPS. Please refer to specific tests for full details, for credentials [3] and other kind of data [2]. Example 1. Basic Authentication over HTTP A typical example is the usage of Basic Authentication over HTTP because with Basic Authentication, after log in, credentials are encoded - and not encrypted - into HTTP Headers. $ 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 compression 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 as-
159 160 Web Application Penetration Testing Web Application Penetration Testing sess 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 Example 3. Checking for Certificate information, Weak Ciphers and SSLv2 via nmap Nmap has two scripts for checking Certificate information, Weak Ciphers and SSLv2 [31]. $ nmap --script ssl-cert,ssl-enum-ciphers -p 443,465,993,995 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 (0.090s latency). rDNS record for 127.0.0.1: www.example.com PORT STATE SERVICE 443/tcp open https | ssl-cert: Subject: commonName=www.example.org | Issuer: commonName=******* | Public Key type: rsa | Public Key bits: 1024 | Not valid before: 2010-01-23T00:00:00+00:00 | Not valid after: 2020-02-28T23:59:59+00:00 | MD5: ******* |_SHA-1: ******* | ssl-enum-ciphers: | SSLv3: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL | TLSv1.0: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL |_ least strength: strong 465/tcp open smtps | ssl-cert: Subject: commonName=*.exapmple.com | Issuer: commonName=******* | Public Key type: rsa | Public Key bits: 2048 | Not valid before: 2010-01-23T00:00:00+00:00 | Not valid after: 2020-02-28T23:59:59+00:00 | MD5: ******* |_SHA-1: ******* | ssl-enum-ciphers: | SSLv3: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL | TLSv1.0: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL |_ least strength: strong 993/tcp open imaps | ssl-cert: Subject: commonName=*.exapmple.com | Issuer: commonName=******* | Public Key type: rsa | Public Key bits: 2048 | Not valid before: 2010-01-23T00:00:00+00:00 | Not valid after: 2020-02-28T23:59:59+00:00 | MD5: ******* |_SHA-1: ******* | ssl-enum-ciphers: | SSLv3: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL | TLSv1.0: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL |_ least strength: strong 995/tcp open pop3s | ssl-cert: Subject: commonName=*.exapmple.com | Issuer: commonName=******* | Public Key type: rsa | Public Key bits: 2048 | Not valid before: 2010-01-23T00:00:00+00:00 | Not valid after: 2020-02-28T23:59:59+00:00 | MD5: ******* |_SHA-1: ******* | ssl-enum-ciphers: | SSLv3: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL | TLSv1.0: | ciphers: | TLS_RSA_WITH_CAMELLIA_128_CBC_SHA - strong | TLS_RSA_WITH_CAMELLIA_256_CBC_SHA - strong | TLS_RSA_WITH_RC4_128_SHA - strong | compressors: | NULL |_ least strength: strong Nmap done: 1 IP address (1 host up) scanned in 8.64 seconds Example 4 Checking for Client-initiated Renegotiation and Secure Renegotiation via openssl (manually) Openssl [30] can be used for testing manually SSL/TLS. In this example the tester tries to initiate a renegotiation by client [m] connecting to server with openssl. The tester then writes the fist line of an HTTP request and types “R” in a new line. He then waits for renegotiaion and completion of the HTTP request and checks if secure renegotiaion is supported by looking at the server output. Using manual requests it is also possible to see if Compression is enabled for TLS and to check for CRIME [13], for ciphers and for other vulnerabilities. $ openssl s_client -connect www2.example.com:443 CONNECTED(00000003) depth=2 ****** verify error:num=20:unable to get local issuer certificate verify return:0 --- Certificate chain 0 s:****** i:****** 1 s:****** i:****** 2 s:****** i:****** --- Server certificate -----BEGIN CERTIFICATE----- ****** -----END CERTIFICATE----- subject=****** issuer=****** --- No client certificate CA names sent --- SSL handshake has read 3558 bytes and written 640 bytes --- New, TLSv1/SSLv3, Cipher is DES-CBC3-SHA Server public key is 2048 bit Secure Renegotiation IS NOT supported Compression: NONE Expansion: NONE SSL-Session: Protocol : TLSv1 Cipher : DES-CBC3-SHA Session-ID: ****** Session-ID-ctx: Master-Key: ****** Key-Arg : None PSK identity: None PSK identity hint: None SRP username: None Start Time: ****** Timeout : 300 (sec) Verify return code: 20 (unable to get local issuer certificate) --- Now the tester can write the first line of an HTTP request and then R in a new line. HEAD / HTTP/1.1 R Server is renegotiating RENEGOTIATING depth=2 C****** verify error:num=20:unable to get local issuer certificate verify return:0
Page 1 and 2:
1 2 THE ICONS BELOW REPRESENT WHAT
Page 3 and 4:
3 4 Testing Guide Frontispiece Test
Page 5 and 6:
7 8 Testing Guide Introduction Test
Page 7 and 8:
11 12 Testing Guide Introduction Te
Page 9 and 10:
15 16 Testing Guide Introduction Te
Page 11 and 12:
19 20 Testing Guide Introduction of
Page 13 and 14:
23 24 Web Application Penetration T
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30: 55 56 Web Application Penetration T
Page 51 and 52: 99 100 Web Application Penetration
Page 79: 155 156 Web Application Penetration
Page 107 and 108: 211 212 Reporting Appendix Test ID
Page 109 and 110: 215 216 Appendix Appendix Testing -
Page 111: 219 220 LDAP Injection For details
show all

1BO4r2U

Create successful ePaper yourself

Delete template?

Save as template?