Started working on explaining the mod_ssl config file.
This commit is contained in:
Eric Christensen
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2 changed files with 23 additions and 128 deletions
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@ -5,8 +5,8 @@
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]>
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<book>
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<xi:include href="Book_Info.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
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<xi:include href="Preface.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
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<xi:include href="Chapter.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
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<!-- <xi:include href="Preface.xml" xmlns:xi="http://www.w3.org/2001/XInclude" /> -->
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<xi:include href="mod_ssl.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
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<xi:include href="Revision_History.xml" xmlns:xi="http://www.w3.org/2001/XInclude" />
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<index />
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</book>
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@ -11,33 +11,19 @@
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<section id="sect-Fedora_Security_Team-Securing_TLS-mod_ssl-configuration">
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<title>Configuration</title>
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<para>
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<application>mod_ssl</application>'s configuration file, by default, appears as such:
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<application>mod_ssl</application>'s configuration file, by default, has mostly sane settings. Below we'll talk about portions of the configuration that are important.
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</para>
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<para>
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<screen>
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#
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# When we also provide SSL we have to listen to the
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# the HTTPS port in addition.
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#
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Listen 443 https
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</screen>
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This specifies the port that httpd should listen to for SSL/TLS traffic. Port 443 is the standard port for https.
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##
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## SSL Global Context
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##
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## All SSL configuration in this context applies both to
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## the main server and all SSL-enabled virtual hosts.
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##
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# Pass Phrase Dialog:
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# Configure the pass phrase gathering process.
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# The filtering dialog program (`builtin' is a internal
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# terminal dialog) has to provide the pass phrase on stdout.
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SSLPassPhraseDialog exec:/usr/libexec/httpd-ssl-pass-dialog
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# Inter-Process Session Cache:
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# Configure the SSL Session Cache: First the mechanism
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# to use and second the expiring timeout (in seconds).
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SSLSessionCache shmcb:/run/httpd/sslcache(512000)
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SSLSessionCacheTimeout 300
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<screen>
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# Pseudo Random Number Generator (PRNG):
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# Configure one or more sources to seed the PRNG of the
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# SSL library. The seed data should be of good random quality.
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@ -53,8 +39,11 @@ SSLRandomSeed connect builtin
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#SSLRandomSeed startup file:/dev/random 512
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#SSLRandomSeed connect file:/dev/random 512
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#SSLRandomSeed connect file:/dev/urandom 512
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</screen>
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#
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The random number generator is very important for cryptology and this is where those settings get established. By default the pseudo-random number generator is defined here although if you have another source of random data you can put that here.
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<screen>
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# Use "SSLCryptoDevice" to enable any supported hardware
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# accelerators. Use "openssl engine -v" to list supported
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# engine names. NOTE: If you enable an accelerator and the
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@ -63,37 +52,29 @@ SSLRandomSeed connect builtin
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#
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SSLCryptoDevice builtin
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#SSLCryptoDevice ubsec
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</screen>
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##
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## SSL Virtual Host Context
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##
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<VirtualHost _default_:443>
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# General setup for the virtual host, inherited from global configuration
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#DocumentRoot "/var/www/html"
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#ServerName www.example.com:443
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# Use separate log files for the SSL virtual host; note that LogLevel
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# is not inherited from httpd.conf.
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ErrorLog logs/ssl_error_log
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TransferLog logs/ssl_access_log
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LogLevel warn
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# SSL Engine Switch:
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# Enable/Disable SSL for this virtual host.
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SSLEngine on
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Many processors have cryptographic accelerators that help with complex ciphers such as AES. In fact, most hardware accelerators are specifically designed to increase the speed of AES-128 (see below where we talk about speed optimization). Unless you have a specific accelerator in your system this default setting should be okay.
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<screen>
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# SSL Protocol support:
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# List the enable protocol levels with which clients will be able to
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# connect. Disable SSLv2 access by default:
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SSLProtocol all -SSLv2
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</screen>
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Here's where the really important settings begin (well, they are all important). SSLProtocol allows you to set which protocols to use (e.g. SSLv2, SSLv3, TLSv1, TLSv1.1, TLSv1.2). The default setting <literal>all -SSLv2</literal> means that all the protocols will be supported except SSLv2. You could go in and individually specify the individual protocols but this setting makes it future-proof. When TLSv1.3 is released and supported by OpenSSL you won't have to change anything; your system will automatically start supporting TLSv1.3. Unless you have a good reason to do so it's recommended that you leave this setting the way it is.
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<screen>
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# SSL Cipher Suite:
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# List the ciphers that the client is permitted to negotiate.
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# See the mod_ssl documentation for a complete list.
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SSLCipherSuite HIGH:MEDIUM:!aNULL:!MD5
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</screen>
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The setting everyone seems to care about. What symmetric ciphers will your webserver will use is determined here. The default setting should probably be hardened a bit by removing <literal>MEDIUM</literal> from the list. All current operating systems and browsers support <literal>HIGH</literal> ciphers which offer the best protection. The <literal>!aNULL</literal> removes unauthenticated cipher options and the <literal>!MD5</literal> removed any cipher that utilizes the <literal>MD5</literal> hash which is quite weak and should be avoided.
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<screen>
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# Speed-optimized SSL Cipher configuration:
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# If speed is your main concern (on busy HTTPS servers e.g.),
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# you might want to force clients to specific, performance
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@ -143,92 +124,6 @@ SSLCertificateKeyFile /etc/pki/tls/private/localhost.key
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# issuer chain before deciding the certificate is not valid.
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#SSLVerifyClient require
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#SSLVerifyDepth 10
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# Access Control:
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# With SSLRequire you can do per-directory access control based
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# on arbitrary complex boolean expressions containing server
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# variable checks and other lookup directives. The syntax is a
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# mixture between C and Perl. See the mod_ssl documentation
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# for more details.
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#<Location />
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#SSLRequire ( %{SSL_CIPHER} !~ m/^(EXP|NULL)/ \
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# and %{SSL_CLIENT_S_DN_O} eq "Snake Oil, Ltd." \
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# and %{SSL_CLIENT_S_DN_OU} in {"Staff", "CA", "Dev"} \
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# and %{TIME_WDAY} >= 1 and %{TIME_WDAY} <= 5 \
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# and %{TIME_HOUR} >= 8 and %{TIME_HOUR} <= 20 ) \
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# or %{REMOTE_ADDR} =~ m/^192\.76\.162\.[0-9]+$/
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#</Location>
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# SSL Engine Options:
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# Set various options for the SSL engine.
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# o FakeBasicAuth:
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# Translate the client X.509 into a Basic Authorisation. This means that
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# the standard Auth/DBMAuth methods can be used for access control. The
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# user name is the `one line' version of the client's X.509 certificate.
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# Note that no password is obtained from the user. Every entry in the user
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# file needs this password: `xxj31ZMTZzkVA'.
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# o ExportCertData:
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# This exports two additional environment variables: SSL_CLIENT_CERT and
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# SSL_SERVER_CERT. These contain the PEM-encoded certificates of the
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# server (always existing) and the client (only existing when client
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# authentication is used). This can be used to import the certificates
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# into CGI scripts.
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# o StdEnvVars:
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# This exports the standard SSL/TLS related `SSL_* ' environment variables.
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# Per default this exportation is switched off for performance reasons,
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# because the extraction step is an expensive operation and is usually
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# useless for serving static content. So one usually enables the
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# exportation for CGI and SSI requests only.
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# o StrictRequire:
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# This denies access when "SSLRequireSSL" or "SSLRequire" applied even
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# under a "Satisfy any" situation, i.e. when it applies access is denied
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# and no other module can change it.
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# o OptRenegotiate:
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# This enables optimized SSL connection renegotiation handling when SSL
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# directives are used in per-directory context.
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#SSLOptions +FakeBasicAuth +ExportCertData +StrictRequire
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<Files ~ "\.(cgi|shtml|phtml|php3?)$">
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SSLOptions +StdEnvVars
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</Files%#62;
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<Directory "/var/www/cgi-bin">
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SSLOptions +StdEnvVars
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</Directory>
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# SSL Protocol Adjustments:
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# The safe and default but still SSL/TLS standard compliant shutdown
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# approach is that mod_ssl sends the close notify alert but doesn't wait for
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# the close notify alert from client. When you need a different shutdown
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# approach you can use one of the following variables:
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# o ssl-unclean-shutdown:
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# This forces an unclean shutdown when the connection is closed, i.e. no
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# SSL close notify alert is send or allowed to received. This violates
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# the SSL/TLS standard but is needed for some brain-dead browsers. Use
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# this when you receive I/O errors because of the standard approach where
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# mod_ssl sends the close notify alert.
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# o ssl-accurate-shutdown:
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# This forces an accurate shutdown when the connection is closed, i.e. a
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# SSL close notify alert is send and mod_ssl waits for the close notify
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# alert of the client. This is 100% SSL/TLS standard compliant, but in
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# practice often causes hanging connections with brain-dead browsers. Use
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# this only for browsers where you know that their SSL implementation
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# works correctly.
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# Notice: Most problems of broken clients are also related to the HTTP
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# keep-alive facility, so you usually additionally want to disable
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# keep-alive for those clients, too. Use variable "nokeepalive" for this.
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# Similarly, one has to force some clients to use HTTP/1.0 to workaround
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# their broken HTTP/1.1 implementation. Use variables "downgrade-1.0" and
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# "force-response-1.0" for this.
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BrowserMatch "MSIE [2-5]" \
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nokeepalive ssl-unclean-shutdown \
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downgrade-1.0 force-response-1.0
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# Per-Server Logging:
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# The home of a custom SSL log file. Use this when you want a
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# compact non-error SSL logfile on a virtual host basis.
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CustomLog logs/ssl_request_log \
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"%t %h %{SSL_PROTOCOL}x %{SSL_CIPHER}x \"%r\" %b"
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</VirtualHost>
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</screen>
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</para>
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</section>
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