Erinevus lehekülje "Modsecurity" redaktsioonide vahel

Allikas: Kuutõrvaja
(→‎Kasutusnäide)
(→‎Reeglite loomine)
149. rida: 149. rida:
 
tõkestatakse ainult liiklus, mis vastab täpselt mingi tuntud ründe
 
tõkestatakse ainult liiklus, mis vastab täpselt mingi tuntud ründe
 
mustrile.
 
mustrile.
 +
 +
Some of the other worms I've seen attempt to use wget to download scripts which they can then execute - so you can block those with:
 +
 +
SecFilter cd\x20/tmp
 +
SecFilter wget\x20
 +
 +
Although we've defined the general action to take against matched rules we can customize the actions on a per-rule basis. For example if we wish we can cause a redirect with the following:
 +
 +
SecFilter /etc/passwd redirect:http://www.foo.com/bad/request.html
 +
 +
Or if we wish we can execute a command to log the request:
 +
 +
SecFilter /bin/rm execute:/usr/local/bin/mail-admin.pl
 +
 +
SecFilter yyy log,exec:/home/ivanr/apache/bin/report-attack.pl
 +
 +
 +
SecFilterSelective THE_REQUEST "/bin/ps"
 +
SecFilterSelective THE_REQUEST "/bin/sh"
 +
SecFilterSelective THE_REQUEST "/tmp/sh"
 +
SecFilterSelective THE_REQUEST "/usr/bin/id"
 +
SecFilterSelective THE_REQUEST "/bin/kill"
 +
SecFilterSelective THE_REQUEST "/usr/bin/gcc"
 +
SecFilterSelective THE_REQUEST "/usr/bin/cc"
 +
SecFilterSelective THE_REQUEST "/usr/bin/g\+\+"
 +
SecFilterSelective THE_REQUEST "/bin/mail"
 +
SecFilterSelective THE_REQUEST "/bin/ls"
 +
 +
Here is an example rule –
 +
 +
 +
SecRule SCRIPT_USERNAME "!^apache$"
 +
 +
In this case, ModSecurity would only allow a script to execute if the owner of the script was the “apache” user.  So, in your scenario, “apache” would not be the owner of perl or sh so this should prevent execution.  You would need to test this with your exact scenario however to see if it works as expected.
 +
  
 
<source lang=apache>
 
<source lang=apache>
−
    # Redirect user on filter match
 
−
    SecFilter xxx redirect:http://www.webkreator.com
 
−
 
−
    # Execute the external script on filter match
 
−
    SecFilter yyy log,exec:/home/ivanr/apache/bin/report-attack.pl
 
 
   
 
   
 
     # Simple filter
 
     # Simple filter
165. rida: 195. rida:
 
     # Only check the body of the POST request
 
     # Only check the body of the POST request
 
     SecFilterSelective POST_PAYLOAD 333
 
     SecFilterSelective POST_PAYLOAD 333
−
+
 
−
    # Only check arguments (will work for GET and POST)
 
−
    SecFilterSelective ARGS 444
 
−
 
−
    # Another test filter, will be denied with 404 but not logged
 
−
    # action supplied as a parameter overrides the default action
 
−
    SecFilter 999 "deny,nolog,status:404"
 
−
 
 
     # Prevent OS specific keywords
 
     # Prevent OS specific keywords
 
     SecFilter /etc/password
 
     SecFilter /etc/password
192. rida: 215. rida:
 
     # Forbid file upload
 
     # Forbid file upload
 
     SecFilterSelective "HTTP_CONTENT_TYPE" multipart/form-data
 
     SecFilterSelective "HTTP_CONTENT_TYPE" multipart/form-data
−
+
 
−
    # Only watch argument p1
 
−
    SecFilterSelective "ARG_p1" 555
 
−
 
−
    # Watch all arguments except p1
 
−
    SecFilterSelective "ARGS|!ARG_p2" 666
 
−
 
 
     # Only allow our own test utility to send requests (or Mozilla)
 
     # Only allow our own test utility to send requests (or Mozilla)
 
     SecFilterSelective HTTP_USER_AGENT "!(mod_security|mozilla)"
 
     SecFilterSelective HTTP_USER_AGENT "!(mod_security|mozilla)"
−
+
 
−
    # Do not allow variables with this name
 
−
    SecFilterSelective ARGS_NAMES 777
 
−
 
−
    # Do now allow this variable value (names are ok)
 
−
    SecFilterSelective ARGS_VALUES 888
 
−
 
 
 
Unixi tavakäskude esinemise keelamine
 
Unixi tavakäskude esinemise keelamine
  

Redaktsioon: 8. mai 2012, kell 16:47

ModSecurity, on nn veebiteenuse tulemüür (Web Application Firewall - WAF) ja IDS/IPS lahendus. Tegemist on tarkvaraga, mis filtreerib veebilehtedele tehtavaid päringuid ja üritab tõkestada nii rünnakuid serverile kui ka lehe näotustamise katseid.

Install ja seadistus

FreeBSDs asub moodul portsude www/mod_security harus Gentoo ...

httpd.conf

Siin on tarvilik laadida moodul ja seejärel konfiguratsioonifail 

LoadModule security_module    modules/mod_security.so

või 

LoadModule security_module /usr/libexec/apache/mod_security.so

Ja 

Include /etc/apache2/modsecurity.conf

modsecurity.conf sisu 

 <IfModule mod_security.c>
    # Enable ModSecurity
    SecFilterEngine On
  
    # Vaikimisi mittesobiv liiklus blokeeritakse, logitakse ja väljastatakse veakood.
    # Tõkestatud liikluse tunnuseks on veakood 403 ja veebilehe asemel
    # ekraanil näidatav kiri pealkirjaga "Forbidden".
    SecFilterDefaultAction "deny,log,status:403"

    #Turn Audit on
    SecAuditEngine On

    SecAuditLog logs/modsec_audit.log 
   
    # Some sane defaults
    SecFilterScanPOST On
    SecFilterCheckURLEncoding On
    SecFilterCheckUnicodeEncoding Off
 
    # buffrite ületäitumise vastu nt SecFilterByteRange 32 126
    # Accept almost all byte values
    SecFilterForceByteRange 1 255
 
    # ei säilita uploaditud faile analüüsiks 
    SecUploadDir /tmp
    SecUploadKeepFiles Off
 
    # Only record the interesting stuff
    SecAuditEngine RelevantOnly
    # Uncomment below to record responses with unusual statuses
    # SecAuditLogRelevantStatus ^5
    
    # modsecurity peamine logifail
    SecAuditLog /var/log/apache2/modsec_audit.log
 
    # You normally won't need debug logging
    SecFilterDebugLevel 0
    # modsecurity debug logi
    SecFilterDebugLog /var/log/apache2/modsec_debug.log
 
    # lokaalne exclude list, ehk siis tühistame mõningad liiga karmid reeglid (süntaks toodud allpool)
    Include /etc/apache2/modsecurity/exclude.conf
 
    # Gotroot.com'i http://www.gotroot.com/ reeglid
    # exclude list
    Include /etc/apache2/modsecurity/gotroot_exclude.conf
    # application protection
    Include /etc/apache2/modsecurity/rules.conf
    #rootkits
    Include /etc/apache2/modsecurity/rootkits.conf
 </IfModule>

deny asemel võib panna ka esialgu debugimise eesmärgil pass.

Veel oleks mõistlik lisada järgnevad asjad: 

 #Accept only valid protocol versions, helps fight HTTP fingerprinting
 SecFilterSelective SERVER_PROTOCOL !^HTTP/(0\.9|1\.0|1\.1)$
 #Allow supported request methods only
 SecFilterSelective REQUEST_METHOD !^(GET|HEAD|POST)$
 #Require HTTP_USER_AGENT and  HTTP_HOST, no telnet use.
 SecFilterSelective "HTTP_USER_AGENT|HTTP_HOST" "^$"
 #require Content-Length to be provided with every POST request.
 SecFilterSelective REQUEST_METHOD ^POST$ chain
 SecFilterSelective HTTP_Content-Length ^$

põhireeglid rules.conf ilmselt kõige mõistlikum. Hetkel küljes ka rootkits.conf, mis peaks tõkestama kõiksugu failide includemised jmt.

badips on 7000~ rida IP numbreid, mida võiks põhimõtteliselt tulemüüri või kuhugi toppida ja ei pea apache regexides kasutama). Ilmselt on mõistlik badips.conf fail küljes hoida juhul kui soov vähendada DDoSi võimalust, kahjuks kõiki maailma halbu aadresse blokeerida ei jõua.

Reeglite uuendamiseks: 

# /usr/local/modsecurity/bin/rules-updater.pl \
-rhttp://www.modsecurity.org/autoupdate/repository/ -p rules -Smodsecurity-crs


/var/log/httpd/modsec_audit.log failist saab jälgida, kelle ta ära blokib. Tundub, et üsna hoogsalt üritatakse spämmi edastada. Kui keegi kurdab, et tal asjad ei tööta, siis tuleks auditi logist uurida ja vajadusel /etc/apache/modsecurity/exclude.conf-is sealsete näidete alusel vastavad ID-d välja lülitada (per LocationMatch või Directory vms).

modsecurity/exclude.conf 

 <Directory /www/html>
 SecFilterRemove 300018
 </Directory>
 
 <Directory /lasteaed/www/html>
 SecFilterRemove 300018
 </Directory>
 
 <Directory /muistne/www/html/>
 SecFilterRemove 300018
 </Directory>

Reegleid saab mõne veebi piires keelata ka näiteks .htaccess fail sisuga 

  SecFilterEngine Off
  SecFilterScanPOST Off

Reeglite loomine

Enamus filtreid rakenduvad HTTP GET päringutele, keelatud on m.h. järgnev:

  • teistele veebilehtedele viitamine täispika URLiga, nagu page=http://www.example.com/
  • SQL käsurea esinemine, nagu: "select * from"
  • UNIXi käskude esinemine, nagu: wget, uname
  • PHP koodi või funktsioonide esinemine, nagu: <?php, exec, fopen

HTTP POST meetodiga saab edastada pikemaid tekste ja faile, mille puhul on raske kindlaks teha, kas tegemist on rünnakuga või näiteks Linuxi installeerimisjuhendiga, mistõttu selle meetodi päringute puhul tõkestatakse ainult liiklus, mis vastab täpselt mingi tuntud ründe mustrile.

Some of the other worms I've seen attempt to use wget to download scripts which they can then execute - so you can block those with: 

SecFilter cd\x20/tmp
SecFilter wget\x20

Although we've defined the general action to take against matched rules we can customize the actions on a per-rule basis. For example if we wish we can cause a redirect with the following: 

SecFilter /etc/passwd redirect:http://www.foo.com/bad/request.html

Or if we wish we can execute a command to log the request: 

SecFilter /bin/rm execute:/usr/local/bin/mail-admin.pl

SecFilter yyy log,exec:/home/ivanr/apache/bin/report-attack.pl


SecFilterSelective THE_REQUEST "/bin/ps" SecFilterSelective THE_REQUEST "/bin/sh" SecFilterSelective THE_REQUEST "/tmp/sh" SecFilterSelective THE_REQUEST "/usr/bin/id" SecFilterSelective THE_REQUEST "/bin/kill" SecFilterSelective THE_REQUEST "/usr/bin/gcc" SecFilterSelective THE_REQUEST "/usr/bin/cc" SecFilterSelective THE_REQUEST "/usr/bin/g\+\+" SecFilterSelective THE_REQUEST "/bin/mail" SecFilterSelective THE_REQUEST "/bin/ls"

Here is an example rule – 


SecRule SCRIPT_USERNAME "!^apache$"

In this case, ModSecurity would only allow a script to execute if the owner of the script was the “apache” user. So, in your scenario, “apache” would not be the owner of perl or sh so this should prevent execution. You would need to test this with your exact scenario however to see if it works as expected. 


 
    # Simple filter
    SecFilter 111
    
    # Only check the QUERY_STRING variable
    SecFilterSelective QUERY_STRING 222
 
    # Only check the body of the POST request
    SecFilterSelective POST_PAYLOAD 333
  
    # Prevent OS specific keywords
    SecFilter /etc/password
  
    # Weaker XSS protection but allows common HTML tags
    SecFilter "<( |\n)*script"
 
    # Prevent XSS atacks (HTML/Javascript injection)
    SecFilter "<(.|\n)+>"
 
    # Very crude filters to prevent SQL injection attacks
    SecFilter "delete[[:space:]]+from"
    SecFilter "insert[[:space:]]+into"
    SecFilter "select.+from"
 
    # Require HTTP_USER_AGENT and HTTP_HOST headers
    SecFilterSelective "HTTP_USER_AGENT|HTTP_HOST" "^$"
 
    # Forbid file upload
    SecFilterSelective "HTTP_CONTENT_TYPE" multipart/form-data
  
    # Only allow our own test utility to send requests (or Mozilla)
    SecFilterSelective HTTP_USER_AGENT "!(mod_security|mozilla)"
  
Unixi tavakäskude esinemise keelamine

 SecFilter (uname|id|ls|cat|rm|kill|mail|su)

Kaustapuus tagasipöördumise keelamiseks, stiilis (../../).

 SecFilter "\.\./"

Keelame unixi failisüsteemi kataloogide kasutamise.

 SecFilter (/home/|/var/|/boot/|/etc/|/bin/|/usr/|/tmp/)

Kasutusnäide

Meil on veeb, mis koosneb failidest.

  • /user_view.php
  • /user_add.php

Tegemist lihtsa veebiga, mis näitab kasutajate nimekirja, lubab sinna kasutajaid lisada ning laadida ka kasutajatest pilte. Kahjuks pole aga veebi kood kuigi hea ja see on kirjutatud üsnagi hulk aega tagasi. Kuidas seda kaitsta pahade kavatsustega inimeste eest?

Võtame ülal viidetud vaikekonfi ja tekitame veebi kaitsmiseks sinna lisaks järgnevad reeglid: 

 <Location /user_view.php>
     # This script only accepts GET
     SecFilterSelective REQUEST_METHOD !^GET$
     # Accept only one parameter: id
     SecFilterSelective ARGS_NAMES !^id$
     # Parameter id is mandatory, and it must be
     # a number, 4-14 digits long
     SecFilterSelective ARG_id !^[[:digit:]]{4,14}$
 </Location>

 <Location /user_add.php>
      # This script only accepts POST
     SecFilterSelective REQUEST_METHOD !^POST$
      # Accept three parameters: firstname, lastname, and email
     SecFilterSelective ARGS_NAMES !^(firstname|lastname|email)$
      # Parameter firstname is mandatory, and it must
      # contain text 1-64 characters long
    SecFilterSelective ARG_firstname !^[[:alnum:][:space:]]{1,64}$
     # Parameter lastname is mandatory, and it must
     # contain text 1-64 characters long
    SecFilterSelective ARG_lastname !^[ [:alnum:][:space:]]{1,64}$
     # Parameter email is optional, but if it is present
     # it must consist only of characters that are
     # allowed in an email address 
    SecFilterSelective ARG_email !(^$|^[[:alnum:].@]{1,64}$)
     # uploadida võib vaid teatud laiendiga faile
    SecFilterSelective POST_PAYLOAD "!image/(jpeg|bmp|gif)"
 </Location>

Märkmeid kasutamisest

rakendamisel default reeglitega tõstis normaalse koormuse juures loadi tunduvalt. Siis kommenteerisin välja suure hulga reegleid, mis spämmisaatmise vastu võitlevad (regexpi kontrollid) ja load jäi 1 ja 1.5 kanti.

Apache 1.3 puhul tasub mod_security kompileerida libpcre abil ja panin apache libpcre sisse laadima - nii ei kasutata enam apache 1.3 seesmist regexi mootorit mis on pcre-st kordades aeglasem.

Lisaks rakenduvad kõigile ülejäänud HTTP päringu päiseridadele filtrid, mis kontrollivad, et need vastaksid standarditele ja ei sisaldaks midagi lubamatut. Normaalse veebiliikluse puhul need reeglid aga probleeme ei peaks tekitama.

Viited

http://www.thebitsource.com/infrastructure-operations/web-application/securing-apache-web-servers-modsecurity/

http://www.askapache.com/htaccess/mod_security-htaccess-tricks.html

http://www.modsecurity.org/documentation/modsecurity-apache/1.9.3/html-multipage/05-actions.html

http://atomicplayboy.net/blog/2005/01/30/an-introduction-to-mod-security/

http://penguinsecurity.net/wiki/index.php?title=Web_Security_Appliance_With_Apache_and_mod_security

http://www.g-loaded.eu/2006/08/24/modsecurity-overview/

Abivahendid

http://www.netnea.com/cms/?q=remo ruulide loomise vahend

http://www.owasp.org/index.php/Category:OWASP_WeBekci_Project haldusvahend

http://www.modsecurity.org/projects/console/index.html ametlik konsool alertide vaatamiseks ja reeglite haldamiseks

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