We have Centos 6.4 server with a physical firewall. We keep seeing quite an number of PHP.CGI.Argument.Injection is detected by the firewall. On the server itself we have done the basic apache hardening as below. We are using fail2ban and also mod_secure. What else can be done to further harden the server? Httpd.conf    #    # This is the main Apache server configuration file.  It contains the    # configuration directives that give the server its instructions.    # See <URL:http://httpd.apache.org/docs/2.2/> for detailed information.    # In particular, see    # <URL:http://httpd.apache.org/docs/2.2/mod/directives.html>    # for a discussion of each configuration directive.    #    #    # Do NOT simply read the instructions in here without understanding    # what they do.  They're here only as hints or reminders.  If you are unsure    # consult the online docs. You have been warned.      #    # The configuration directives are grouped into three basic sections:    #  1. Directives that control the operation of the Apache server process as a    #     whole (the 'global environment').    #  2. Directives that define the parameters of the 'main' or 'default' server,    #     which responds to requests that aren't handled by a virtual host.    #     These directives also provide default values for the settings    #     of all virtual hosts.    #  3. Settings for virtual hosts, which allow Web requests to be sent to    #     different IP addresses or hostnames and have them handled by the    #     same Apache server process.    #    # Configuration and logfile names: If the filenames you specify for many    # of the server's control files begin with / (or drive:/ for Win32), the    # server will use that explicit path.  If the filenames do *not* begin    # with /, the value of ServerRoot is prepended -- so logs/foo.log    # with ServerRoot set to /etc/httpd will be interpreted by the    # server as /etc/httpd/logs/foo.log.    #    ### Section 1: Global Environment    #    # The directives in this section affect the overall operation of Apache,    # such as the number of concurrent requests it can handle or where it    # can find its configuration files.    #    #    # Don't give away too much information about all the subcomponents    # we are running.  Comment out this line if you don't mind remote sites    # finding out what major optional modules you are running    ServerTokens OS    #    # ServerRoot: The top of the directory tree under which the server's    # configuration, error, and log files are kept.    #    # NOTE!  If you intend to place this on an NFS (or otherwise network)    # mounted filesystem then please read the LockFile documentation    # (available at <URL:http://httpd.apache.org/docs/2.2/mod/mpm_common.html#lockfile>);    # you will save yourself a lot of trouble.    #    # Do NOT add a slash at the end of the directory path.    #    ServerRoot /etc/httpd    #    # PidFile: The file in which the server should record its process    # identification number when it starts.  Note the PIDFILE variable in    # /etc/sysconfig/httpd must be set appropriately if this location is    # changed.    #    PidFile run/httpd.pid    #    # Timeout: The number of seconds before receives and sends time out.    #    Timeout 60    #    # KeepAlive: Whether or not to allow persistent connections (more than    # one request per connection). Set to Off to deactivate.    #    KeepAlive Off    #    # MaxKeepAliveRequests: The maximum number of requests to allow    # during a persistent connection. Set to 0 to allow an unlimited amount.    # We recommend you leave this number high, for maximum performance.    #    MaxKeepAliveRequests 100    #    # KeepAliveTimeout: Number of seconds to wait for the next request from the    # same client on the same connection.    #    KeepAliveTimeout 15    ##    ## Server-Pool Size Regulation (MPM specific)    ##     # prefork MPM    # StartServers: number of server processes to start    # MinSpareServers: minimum number of server processes which are kept spare    # MaxSpareServers: maximum number of server processes which are kept spare    # ServerLimit: maximum value for MaxClients for the lifetime of the server    # MaxClients: maximum number of server processes allowed to start    # MaxRequestsPerChild: maximum number of requests a server process serves    <IfModule prefork.c>    StartServers       8    MinSpareServers    5    MaxSpareServers   20    ServerLimit      256    MaxClients       256    MaxRequestsPerChild  4000    </IfModule>    # worker MPM    # StartServers: initial number of server processes to start    # MaxClients: maximum number of simultaneous client connections    # MinSpareThreads: minimum number of worker threads which are kept spare    # MaxSpareThreads: maximum number of worker threads which are kept spare    # ThreadsPerChild: constant number of worker threads in each server process    # MaxRequestsPerChild: maximum number of requests a server process serves    <IfModule worker.c>    StartServers         4    MaxClients         300    MinSpareThreads     25    MaxSpareThreads     75     ThreadsPerChild     25    MaxRequestsPerChild  0    </IfModule>    #    # Listen: Allows you to bind Apache to specific IP addresses and/or    # ports, in addition to the default. See also the <VirtualHost>    # directive.    #    # Change this to Listen on specific IP addresses as shown below to     # prevent Apache from glomming onto all bound IP addresses (0.0.0.0)    #    #Listen 12.34.56.78:80    Listen 80    #    # Dynamic Shared Object (DSO) Support    #    # To be able to use the functionality of a module which was built as a DSO you    # have to place corresponding `LoadModule' lines at this location so the    # directives contained in it are actually available _before_ they are used.    # Statically compiled modules (those listed by `httpd -l') do not need    # to be loaded here.    #    # Example:    # LoadModule foo_module modules/mod_foo.so    #    #LoadModule auth_basic_module modules/mod_auth_basic.so    #LoadModule auth_digest_module modules/mod_auth_digest.so    #LoadModule authn_file_module modules/mod_authn_file.so    #LoadModule authn_alias_module modules/mod_authn_alias.so    #LoadModule authn_anon_module modules/mod_authn_anon.so    #LoadModule authn_dbm_module modules/mod_authn_dbm.so    #LoadModule authn_default_module modules/mod_authn_default.so    #LoadModule authz_host_module modules/mod_authz_host.so    #LoadModule authz_user_module modules/mod_authz_user.so    #LoadModule authz_owner_module modules/mod_authz_owner.so    #LoadModule authz_groupfile_module modules/mod_authz_groupfile.so    #LoadModule authz_dbm_module modules/mod_authz_dbm.so    LoadModule authz_default_module modules/mod_authz_default.so    LoadModule ldap_module modules/mod_ldap.so    LoadModule authnz_ldap_module modules/mod_authnz_ldap.so    LoadModule include_module modules/mod_include.so    LoadModule log_config_module modules/mod_log_config.so    LoadModule logio_module modules/mod_logio.so    LoadModule env_module modules/mod_env.so    LoadModule ext_filter_module modules/mod_ext_filter.so    LoadModule mime_magic_module modules/mod_mime_magic.so    LoadModule expires_module modules/mod_expires.so    LoadModule deflate_module modules/mod_deflate.so    LoadModule headers_module modules/mod_headers.so    LoadModule usertrack_module modules/mod_usertrack.so    LoadModule setenvif_module modules/mod_setenvif.so    LoadModule mime_module modules/mod_mime.so    #LoadModule dav_module modules/mod_dav.so    LoadModule status_module modules/mod_status.so    LoadModule autoindex_module modules/mod_autoindex.so    LoadModule info_module modules/mod_info.so    #LoadModule dav_fs_module modules/mod_dav_fs.so    LoadModule vhost_alias_module modules/mod_vhost_alias.so    #LoadModule negotiation_module modules/mod_negotiation.so    LoadModule dir_module modules/mod_dir.so    LoadModule actions_module modules/mod_actions.so    #LoadModule speling_module modules/mod_speling.so    LoadModule userdir_module modules/mod_userdir.so    LoadModule alias_module modules/mod_alias.so    #LoadModule substitute_module modules/mod_substitute.so    LoadModule rewrite_module modules/mod_rewrite.so    #LoadModule proxy_module modules/mod_proxy.so    #LoadModule proxy_balancer_module modules/mod_proxy_balancer.so    #LoadModule proxy_ftp_module modules/mod_proxy_ftp.so    #LoadModule proxy_http_module modules/mod_proxy_http.so    #LoadModule proxy_ajp_module modules/mod_proxy_ajp.so    #LoadModule proxy_connect_module modules/mod_proxy_connect.so    LoadModule cache_module modules/mod_cache.so    LoadModule suexec_module modules/mod_suexec.so    LoadModule disk_cache_module modules/mod_disk_cache.so    LoadModule cgi_module modules/mod_cgi.so    LoadModule version_module modules/mod_version.so    #    # The following modules are not loaded by default:    #    #LoadModule asis_module modules/mod_asis.so    #LoadModule authn_dbd_module modules/mod_authn_dbd.so    #LoadModule cern_meta_module modules/mod_cern_meta.so    #LoadModule cgid_module modules/mod_cgid.so    #LoadModule dbd_module modules/mod_dbd.so    #LoadModule dumpio_module modules/mod_dumpio.so    #LoadModule filter_module modules/mod_filter.so    #LoadModule ident_module modules/mod_ident.so    #LoadModule log_forensic_module modules/mod_log_forensic.so    #LoadModule unique_id_module modules/mod_unique_id.so    #    #    # Load config files from the config directory /etc/httpd/conf.d.    #    Include conf.d/*.conf    #    #ExtendedStatus On    #    #    User apache    Group apache    #    ServerAdmin root@localhost           #    # If your host doesn't have a registered DNS name, enter its IP address here.    # You will have to access it by its address anyway, and this will make     # redirections work in a sensible way.    #ServerName http://********:80    # ServerName directive.    #    UseCanonicalName Off           #    DocumentRoot /var/www/html    # First, we configure the default to be a very restrictive set of     # features.      #    <Directory />        Options FollowSymLinks        AllowOverride None    </Directory>    <Directory /var/www/html>    #        Options -Indexes FollowSymLinks    #        AllowOverride None    #    # Controls who can get stuff from this server.    #        Order allow,deny        Allow from all    </Directory>            #    # See also: http://httpd.apache.org/docs/misc/FAQ.html#forbidden    #    <IfModule mod_userdir.c>        #        UserDir disabled        #         #UserDir public_html    </IfModule>    DirectoryIndex index.html index.html.var    #    # AccessFileName: The name of the file to look for in each directory    # for additional configuration directives.  See also the AllowOverride    # directive.    #    AccessFileName .htaccess    #    # The following lines prevent .htaccess and .htpasswd files from being     # viewed by Web clients.     #    <Files ~ ^\.ht>        Order allow,deny        Deny from all        Satisfy All    </Files>    #    # TypesConfig describes where the mime.types file (or equivalent) is    # to be found.    #    TypesConfig /etc/mime.types    # a good value.  If most of your content is binary, such as applications    # or images, you may want to use application/octet-stream instead to    # keep browsers from trying to display binary files as though they are    # text.    #    DefaultType text/plain    # contents of the file itself to determine its type.  The MIMEMagicFile    # directive tells the module where the hint definitions are located.    #    <IfModule mod_mime_magic.c>    #   MIMEMagicFile /usr/share/magic.mime        MIMEMagicFile conf/magic    </IfModule>    # nameserver.    #    HostnameLookups Off    #    #EnableMMAP off    #    #EnableSendfile off    #    ErrorLog logs/error_log    LogLevel warn    LogFormat %h %l %u %t \%r\ %>s %b \%{Referer}i\ \%{User-Agent}i\ combined    LogFormat %h %l %u %t \%r\ %>s %b common    LogFormat %{Referer}i -> %U referer    LogFormat %{User-agent}i agent    # combinedio includes actual counts of actual bytes received (%I) and sent (%O); this    # requires the mod_logio module to be loaded.    #LogFormat %h %l %u %t \%r\ %>s %b \%{Referer}i\ \%{User-Agent}i\ %I %O combinedio    #    #CustomLog logs/access_log common    #    # If you would like to have separate agent and referer logfiles, uncomment    # the following directives.    #    #CustomLog logs/referer_log referer    #CustomLog logs/agent_log agent    CustomLog logs/access_log combined    # Set to EMail to also include a mailto: link to the ServerAdmin.    # Set to one of:  On | Off | EMail    #    ServerSignature Off    # We include the /icons/ alias for FancyIndexed directory listings.  If you    # do not use FancyIndexing, you may comment this out.    #    Alias /icons/ /var/www/icons/    <Directory /var/www/icons>        Options Indexes MultiViews FollowSymLinks        AllowOverride None        Order allow,deny        Allow from all    </Directory>    #    # WebDAV module configuration section.    #     <IfModule mod_dav_fs.c>        # Location of the WebDAV lock database.        DAVLockDB /var/lib/dav/lockdb    </IfModule>    ScriptAlias /cgi-bin/ /var/www/cgi-bin/    #    # /var/www/cgi-bin should be changed to whatever your ScriptAliased    # CGI directory exists, if you have that configured.    #    <Directory /var/www/cgi-bin>        AllowOverride None        Options None        Order allow,deny        Allow from all    </Directory>    IndexOptions FancyIndexing VersionSort NameWidth=* HTMLTable Charset=UTF-8    AddIconByEncoding (CMP,/icons/compressed.gif) x-compress x-gzip    AddIconByType (TXT,/icons/text.gif) text/*    AddIconByType (IMG,/icons/image2.gif) image/*    AddIconByType (SND,/icons/sound2.gif) audio/*    AddIconByType (VID,/icons/movie.gif) video/*    AddIcon /icons/binary.gif .bin .exe    AddIcon /icons/binhex.gif .hqx    AddIcon /icons/tar.gif .tar    AddIcon /icons/world2.gif .wrl .wrl.gz .vrml .vrm .iv    AddIcon /icons/compressed.gif .Z .z .tgz .gz .zip    AddIcon /icons/a.gif .ps .ai .eps    AddIcon /icons/layout.gif .html .shtml .htm .pdf    AddIcon /icons/text.gif .txt    AddIcon /icons/c.gif .c    AddIcon /icons/p.gif .pl .py    AddIcon /icons/f.gif .for    AddIcon /icons/dvi.gif .dvi    AddIcon /icons/uuencoded.gif .uu    AddIcon /icons/script.gif .conf .sh .shar .csh .ksh .tcl    AddIcon /icons/tex.gif .tex    AddIcon /icons/bomb.gif core    AddIcon /icons/back.gif ..    AddIcon /icons/hand.right.gif README    AddIcon /icons/folder.gif ^^DIRECTORY^^    AddIcon /icons/blank.gif ^^BLANKICON^^    #    # DefaultIcon is which icon to show for files which do not have an icon    # explicitly set.    #    DefaultIcon /icons/unknown.gif    # HeaderName is the name of a file which should be prepended to    # directory indexes.     ReadmeName README.html    HeaderName HEADER.html    #    # IndexIgnore is a set of filenames which directory indexing should ignore    # and not include in the listing.  Shell-style wildcarding is permitted.    #    IndexIgnore .??* *~ *# HEADER* README* RCS CVS *,v *,t    # * being a certain language than marking it with the wrong    # * language!    #    DefaultLanguage english    # Simplified Chinese (zh-CN) - Spanish (es) - Traditional Chinese (zh-TW)    #    AddLanguage ca .ca    AddLanguage cs .cz .cs    AddLanguage da .dk    AddLanguage de .de    AddLanguage el .el    AddLanguage en .en    AddLanguage eo .eo    AddLanguage es .es    AddLanguage et .et    AddLanguage fr .fr    AddLanguage he .he    AddLanguage hr .hr    AddLanguage it .it    AddLanguage ja .ja    AddLanguage ko .ko    AddLanguage ltz .ltz    AddLanguage nl .nl    AddLanguage nn .nn    AddLanguage no .no    AddLanguage pl .po    AddLanguage pt .pt    AddLanguage pt-BR .pt-br    AddLanguage ru .ru    AddLanguage sv .sv    AddLanguage zh-CN .zh-cn    AddLanguage zh-TW .zh-tw    LanguagePriority en ca cs da de el eo es et fr he hr it ja ko ltz nl nn no pl pt pt-BR ru sv zh-CN zh-TW    ForceLanguagePriority Prefer Fallback    AddDefaultCharset UTF-8    #    # AddType allows you to add to or override the MIME configuration    # file mime.types for specific file types.    #    #AddType application/x-tar .tgz    #    # AddEncoding allows you to have certain browsers uncompress    # information on the fly. Note: Not all browsers support this.    #AddEncoding x-compress .Z    #AddEncoding x-gzip .gz .tgz    # If the AddEncoding directives above are commented-out, then you    # probably should define those extensions to indicate media types:    #    AddType application/x-compress .Z    AddType application/x-gzip .gz .tgz    #    #   MIME-types for downloading Certificates and CRLs    #    AddType application/x-x509-ca-cert .crt    AddType application/x-pkcs7-crl    .crl    #    # AddHandler allows you to map certain file extensions to handlers:    # actions unrelated to filetype. These can be either built into the server    # or added with the Action directive (see below)    #    # To use CGI scripts outside of ScriptAliased directories:    # (You will also need to add ExecCGI to the Options directive.)    #    #AddHandler cgi-script .cgi    #    # For files that include their own HTTP headers:    #    #AddHandler send-as-is asis    #    # For type maps (negotiated resources):    # (This is enabled by default to allow the Apache It Worked page    #  to be distributed in multiple languages.)    #    AddHandler type-map var    #    # Filters allow you to process content before it is sent to the client.    #    # To parse .shtml files for server-side includes (SSI):    # (You will also need to add Includes to the Options directive.)    #    AddType text/html .shtml    AddOutputFilter INCLUDES .shtml    # Action lets you define media types that will execute a script whenever    # Format: Action media/type /cgi-script/location    # Format: Action handler-name /cgi-script/location    #    # Some examples:    #ErrorDocument 500 The server made a boo boo.    #ErrorDocument 404 /missing.html    #ErrorDocument 404 /cgi-bin/missing_handler.pl    #ErrorDocument 402 http://www.example.com/subscription_info.html    #    #    # Putting this all together, we can internationalize error responses.    #    # We use Alias to redirect any /error/HTTP_<error>.html.var response to    # our collection of by-error message multi-language collections.  We use     # includes to substitute the appropriate text.    #    # You can modify the messages' appearance without changing any of the    # default HTTP_<error>.html.var files by adding the line:    #    #   Alias /error/include/ /your/include/path/    #    # which allows you to create your own set of files by starting with the    # /var/www/error/include/ files and    # copying them to /your/include/path/, even on a per-VirtualHost basis.    #    Alias /error/ /var/www/error/    <IfModule mod_negotiation.c>    <IfModule mod_include.c>        <Directory /var/www/error>            AllowOverride None            Options IncludesNoExec            AddOutputFilter Includes html            AddHandler type-map var            Order allow,deny            Allow from all            LanguagePriority en es de fr            ForceLanguagePriority Prefer Fallback        </Directory>    #    ErrorDocument 400 /error/HTTP_BAD_REQUEST.html.var    #    ErrorDocument 401 /error/HTTP_UNAUTHORIZED.html.var    #    ErrorDocument 403 /error/HTTP_FORBIDDEN.html.var    #    ErrorDocument 404 /error/HTTP_NOT_FOUND.html.var    #    ErrorDocument 405 /error/HTTP_METHOD_NOT_ALLOWED.html.var    #    ErrorDocument 408 /error/HTTP_REQUEST_TIME_OUT.html.var    #    ErrorDocument 410 /error/HTTP_GONE.html.var    #    ErrorDocument 411 /error/HTTP_LENGTH_REQUIRED.html.var    #    ErrorDocument 412 /error/HTTP_PRECONDITION_FAILED.html.var    #    ErrorDocument 413 /error/HTTP_REQUEST_ENTITY_TOO_LARGE.html.var    #    ErrorDocument 414 /error/HTTP_REQUEST_URI_TOO_LARGE.html.var    #    ErrorDocument 415 /error/HTTP_UNSUPPORTED_MEDIA_TYPE.html.var    #    ErrorDocument 500 /error/HTTP_INTERNAL_SERVER_ERROR.html.var    #    ErrorDocument 501 /error/HTTP_NOT_IMPLEMENTED.html.var    #    ErrorDocument 502 /error/HTTP_BAD_GATEWAY.html.var    #    ErrorDocument 503 /error/HTTP_SERVICE_UNAVAILABLE.html.var    #    ErrorDocument 506 /error/HTTP_VARIANT_ALSO_VARIES.html.var    </IfModule>    </IfModule>    #    # The following directives modify normal HTTP response behavior to    # handle known problems with browser implementations.    #    BrowserMatch Mozilla/2 nokeepalive    BrowserMatch MSIE 4\.0b2; nokeepalive downgrade-1.0 force-response-1.0    BrowserMatch RealPlayer 4\.0 force-response-1.0    BrowserMatch Java/1\.0 force-response-1.0    BrowserMatch JDK/1\.0 force-response-1.0    #    # The following directive disables redirects on non-GET requests for    # a directory that does not include the trailing slash.  This fixes a     # problem with Microsoft WebFolders which does not appropriately handle     # redirects for folders with DAV methods.    # Same deal with Apple's DAV filesystem and Gnome VFS support for DAV.    #    BrowserMatch Microsoft Data Access Internet Publishing Provider redirect-carefully    BrowserMatch MS FrontPage redirect-carefully    BrowserMatch ^WebDrive redirect-carefully    BrowserMatch ^WebDAVFS/1.[0123] redirect-carefully    BrowserMatch ^gnome-vfs/1.0 redirect-carefully    BrowserMatch ^XML Spy redirect-carefully    BrowserMatch ^Dreamweaver-WebDAV-SCM1 redirect-carefully
Minimize PHP.CGI.Argument.Injection and further hardening of the Centos 6.4 web server
centos;security;apache httpd;php
Penetration TestingWhen maintaining a server that's accessible to the internet you really can't escape the need to perform penetration testing (aka. pentesting) yourself. I typically use the following tools to do this:OpenVAS is a framework of several services and tools offering a comprehensive and powerful vulnerability scanning and vulnerability management solution. (Free/Opensource)http://www.openvas.org/Nessus is a proprietary comprehensive vulnerability scanner which is developed by Tenable Network Security. It is free of charge for personal use in a non-enterprise environment. Its goal is to detect potential vulnerabilities on the tested systems.http://www.tenable.com/products/nessusMetasploit Framework is a tool for developing and executing exploit code against a remote target machine.http://www.metasploit.com/NSA Hardening GuideI typically go through this guide when setting up a CentOS system. It's specific to RHEL5 but everything in the guide is relevant and should be adhered to. It does specifically discuss hardening Apache.Guide to the Secure Conguration of Red Hat Enterprise Linux 5 - NSAAuditingAs you're doing now, review any anomalies and follow up on them and make sure you understand them so that you can weigh whether they're a potential vector for your setup or not.Eric Romang's Blog is a pretty good resource for looking these vulnerabilities up. Specifically here's the exploit you're noticing: CVE-2012-1823 PHP CGI Argument Injection Metasploit Demo. You can also look up the vulnerabilities in these 2 databases:OSVDB - Open Sourced Vulnerability DatabaseCVE - Common Vulnerabilities and Exposures List