!'UIDETO"UILDING3ECURE7EB!PPLICATIONS

phpwind  时间:2021-02-13  阅读:()
!
'UIDET#HRIS3HImETT%SSENTIAL0(03ECURITY%SSENTIAL03ECURITYThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
40Chapter4CHAPTER4SessionsandCookiesThischapterdiscussessessionsandtheinherentrisksassociatedwithstatefulwebapplications.
Youwillfirstlearnthefundamentalsofstate,cookies,andsessions;thenIwilldiscussseveralconcerns—cookietheft,exposedsessiondata,sessionfixa-tion,andsessionhijacking—alongwithpracticesthatyoucanemploytohelppre-ventthem.
Therumorsaretrue:HTTPisastatelessprotocol.
ThisdescriptionrecognizesthelackofassociationbetweenanytwoHTTPrequests.
Becausetheprotocoldoesnotprovideanymethodthattheclientcanusetoidentifyitself,theservercannotdistin-guishbetweenclients.
WhilethestatelessnatureofHTTPhassomeimportantbenefits—afterall,maintain-ingstaterequiressomeoverhead—itpresentsauniquechallengetodeveloperswhoneedtocreatestatefulwebapplications.
Withnowaytoidentifytheclient,itisimpossibletodeterminewhethertheuserisalreadyloggedin,hasitemsinashop-pingcart,orneedstoregister.
Anelegantsolutiontothisproblem,originallyconceivedbyNetscape,isastateman-agementmechanismcalledcookies.
CookiesareanextensionoftheHTTPprotocol.
Moreprecisely,theyconsistoftwoHTTPheaders:theSet-CookieresponseheaderandtheCookierequestheader.
WhenaclientsendsarequestforaparticularURL,theservercanopttoincludeaSet-Cookieheaderintheresponse.
Thisisarequestfortheclienttoincludeacorre-spondingCookieheaderinitsfuturerequests.
Figure4-1illustratesthisbasicexchange.
Ifyouusethisconcepttoallowauniqueidentifiertobeincludedineachrequest(inaCookieheader),youcanbegintouniquelyidentifyclientsandassociatetheirrequeststogether.
Thisisallthatisrequiredforstate,andthisistheprimaryuseofthemechanism.
,ch04.
847Page40Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
CookieTheft|41ThebestreferenceforcookiesisstillthespecificationprovidedbyNetscapeathttp://wp.
netscape.
com/newsref/std/cookie_spec.
html.
Thismostcloselyresemblesindustrysupport.
Theconceptofsessionmanagementbuildsupontheabilitytomaintainstatebymaintainingdataassociatedwitheachuniqueclient.
Thisdataiskeptinasessiondatastore,anditisupdatedoneachrequest.
Becausetheuniqueidentifierspecifiesaparticularrecordinthesessiondatastore,it'smostoftencalledthesessionidentifier.
IfyouusePHP'snativesessionmechanism,allofthiscomplexityishandledforyou.
Whenyoucallsession_start(),PHPfirstdetermineswhetherasessionidentifierisincludedinthecurrentrequest.
Ifoneis,thesessiondataforthatparticularsessionisreadandprovidedtoyouinthe$_SESSIONsuperglobalarray.
Ifoneisnot,PHPgeneratesasessionidentifierandcreatesanewrecordinthesessiondatastore.
Italsohandlespropagatingthesessionidentifierandupdatingthesessiondatastoreoneachrequest.
Figure4-2illustratesthisprocess.
Whilethisconvenienceishelpful,itisimportanttorealizethatitisnotacompletesolution.
ThereisnoinherentsecurityinPHP'ssessionmechanism,asidefromthefactthatthesessionidentifieritgeneratesissufficientlyrandom,therebyeliminatingthepracticalityofprediction.
Youmustprovideyourownsafeguardstoprotectagainstallothersessionattacks.
Iwillshowyouafewproblemsandsolutionsinthischapter.
CookieTheftOneriskassociatedwiththeuseofcookiesisthatauser'scookiescanbestolenbyanattacker.
Ifthesessionidentifieriskeptinacookie,cookiedisclosureisaseriousrisk,becauseitcanleadtosessionhijacking.
Figure4-1.
AcompletecookieexchangethatinvolvestwoHTTPtransactionsClientServer1HTTPrequestHTTPresponse&Set-Cookie2HTTPrequest&CookieHTTPresponse,ch04.
847Page41Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
42|Chapter4:SessionsandCookiesThetwomostcommoncausesofcookiedisclosurearebrowservulnerabilitiesandcross-sitescripting(discussedinChapter2).
Whilenosuchbrowservulnerabilitiesareknownatthistime,therehavebeenafewinthepast—themostnotableonesareinInternetExplorerVersions4.
0,5.
0,5.
5,and6.
0(correctivepatchesareavailableforeachofthesevulnerabilities).
Whilebrowservulnerabilitiesarecertainlynotthefaultofwebdevelopers,youmaybeabletotakestepstomitigatetherisktoyourusers.
Insomecases,youmaybeabletoimplementsafeguardsthatpracticallyeliminatetherisk.
Attheveryleast,youcantrytoeducateyourusersanddirectthemtoapatchtofixthevulnerability.
Forthesereasons,itisgoodtobeawareofnewvulnerabilities.
Thereareafewwebsitesandmailingliststhatyoucankeepupwith,andmanyservicesarebeginningtoofferRSSfeeds,sothatyoucansimplysubscribetothefeedandbealertedtonewvulnerabilities.
SecurityFocusmaintainsalistofsoftwarevulnerabilitiesathttp://online.
securityfocus.
com/vulnerabilities,andyoucanfiltertheseadvisoriesbyvendor,title,andversion.
ThePHPSecurityConsortiumalsomaintainssummariesoftheSecurityFocusnewslettersathttp://phpsec.
org/projects/vulnerabilities/securityfocus.
html.
Figure4-2.
PHPhandlesthecomplexityofsessionmanagementforyouPHPSESSIDincookiePHPSESSIDinquerystringGeneratenewPHPSESSIDFetchsessiondataandpopulate$_SESSIONSetcookieandcachingheadersRewriteURLSStoresessiondataNoYesYesCodePHP,ch04.
847Page42Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
SessionFixation|43Cross-sitescriptingisamorecommonapproachusedbyattackerstostealcookies.
Anattackercanuseseveralapproaches,oneofwhichisdescribedinChapter2.
Becauseclient-sidescriptshaveaccesstocookies,allanattackermustdoiswriteascriptthatdeliversthisinformation.
Creativityistheonlylimitingfactor.
Protectingyourusersfromcookietheftisthereforeacombinationofavoidingcross-sitescriptingvulnerabilitiesanddetectingbrowserswithsecurityvulnerabilitiesthatcanleadtocookieexposure.
Becausethelatterissouncommon(withanyluck,thesetypesofvulnerabilitieswillremainararity),itisnottheprimaryconcernbutrathersomethingtokeepinmind.
ExposedSessionDataSessiondataoftenconsistsofpersonalinformationandothersensitivedata.
Forthisreason,theexposureofsessiondataisacommonconcern.
Ingeneral,theexposureisminimal,becausethesessiondatastoreresidesintheserverenvironment,whetherinadatabaseorthefilesystem.
Therefore,sessiondataisnotinherentlysubjecttopublicexposure.
EnablingSSLisaparticularlyusefulwaytominimizetheexposureofdatabeingsentbetweentheclientandtheserver,andthisisveryimportantforapplicationsthatexchangesensitivedatawiththeclient.
SSLprovidesalayerofsecuritybeneathHTTP,sothatalldatawithinHTTPrequestsandresponsesisprotected.
Ifyouareconcernedaboutthesecurityofthesessiondatastoreitself,youcanencryptitsothatsessiondatacannotbereadwithouttheappropriatekey.
ThisismosteasilyachievedinPHPbyusingsession_set_save_handler()andwritingyourownsessionstorageandretrievalfunctionsthatencryptsessiondatabeingstoredanddecryptsessiondatabeingread.
SeeAppendixCformoreinformationaboutencryptingasessiondatastore.
SessionFixationAmajorconcernregardingsessionsisthesecrecyofthesessionidentifier.
Ifthisiskeptsecret,thereisnopracticalriskofsessionhijacking.
Withavalidsessionidenti-fier,anattackerismuchmorelikelytosuccessfullyimpersonateoneofyourusers.
Anattackercanusethreeprimarymethodstoobtainavalidsessionidentifier:PredictionCaptureFixation,ch04.
847Page43Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
44|Chapter4:SessionsandCookiesPHPgeneratesaveryrandomsessionidentifier,sopredictionisnotapracticalrisk.
Capturingasessionidentifierismorecommon—minimizingtheexposureoftheses-sionidentifier,usingSSL,andkeepingupwithbrowservulnerabilitiescanhelpyoumitigatetheriskofcapture.
KeepinmindthatabrowserincludesaCookieheaderinallrequeststhatsatisfytherequirementssetforthinapreviousSet-Cookieheader.
Quitecommonly,thesessionidentifierisbeingexposedunnecessarilyinrequestsforembeddedresources,suchasimages.
Forexample,torequestawebpagewith10images,thesessionidentifierisbeingsentbythebrowserin11differentrequests,butitisneededforonly1ofthose.
Toavoidthisunnecessaryexposure,youmightconsiderserv-ingallembeddedresourcesfromaserverwithadifferentdomainname.
Sessionfixationisanattackthattricksthevictimintousingasessionidentifiercho-senbytheattacker.
Itisthesimplestmethodbywhichtheattackercanobtainavalidsessionidentifier.
Inthesimplestcase,asessionfixationattackusesalink:ClickHereAnotherapproachistouseaprotocol-levelredirect:TheRefreshheadercanalsobeused—providedasanactualHTTPheaderorinthehttp-equivattributeofametatag.
Theattacker'sgoalistogettheusertovisitaURLthatincludesasessionidentifieroftheattacker'schoosing.
Thisisthefirststepinabasicattack;thecompleteattackisillustratedinFigure4-3.
Figure4-3.
AsessionfixationattackusesasessionidentifierchosenbytheattackerVictimexample.
org123target.
example.
orgGET/login.
phpPHPSESSID=123HTTP/1.
1HOST:target.
example.
orgClickHere,ch04.
847Page44Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
SessionFixation|45Ifsuccessful,theattackerisabletoavoidthenecessityofcapturingorpredictingavalidsessionidentifier,anditispossibletolaunchadditionalandmoredangeroustypesofattacks.
Agoodwaytobetterunderstandthisistotryityourself.
Beginwithascriptnamedfixation.
php:Ensurethatyoudonothaveanyexistingcookiesforthecurrenthost,orclearallcookiestobecertain.
Visitfixation.
phpandincludePHPSESSIDintheURL:http://example.
org/fixation.
phpPHPSESSID=1234Thiscreatesasessionvariable(username)withavalueofchris.
Aninspectionofthesessiondatastorerevealsthat1234isthesessionidentifierassociatedwiththisdata:$cat/tmp/sess_1234username|s:5:"chris";Createasecondscript,test.
php,thatoutputsthevalueof$_SESSION['username']ifitexists:VisitthisURLusingadifferentcomputer,oratleastadifferentbrowser,andincludethesamesessionidentifierintheURL:http://example.
org/test.
phpPHPSESSID=1234Thiscausesyoutoresumethesessionyoubeganwhenyouvisitedfixation.
php,andtheuseofadifferentcomputer(ordifferentbrowser)mimicsanattacker'sposition.
Youhavesuccessfullyhijackedasession,andthisisexactlywhatanattackercando.
Clearly,thisisnotdesirable.
Becauseofthisbehavior,anattackercanprovidealinktoyourapplication,andanyonewhousesthislinktovisityoursitewilluseasessionidentifierchosenbytheattacker.
,ch04.
847Page45Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
46|Chapter4:SessionsandCookiesOnecauseofthisproblemisthatasessionidentifierintheURLisusedtocreateanewsession—evenwhenthereisnoexistingsessionforthatparticularsessioniden-tifier,PHPcreatesone.
Thisprovidesaconvenientopeningforanattacker.
Luckily,thesession_regenerate_id()functioncanbeusedtohelppreventthis:Thisensuresthatafreshsessionidentifierisusedwheneverasessionisinitiated.
However,thisisnotaneffectivesolutionbecauseasessionfixationattackcanstillbesuccessful.
Theattackercansimplyvisityourwebsite,determinethesessionidenti-fierthatPHPassigns,andusethatsessionidentifierinthesessionfixationattack.
Thisdoeseliminatetheopportunityforanattackertoassignasimplesessionidenti-fiersuchas1234,buttheattackercanstillexaminethecookieorURL(dependinguponthemethodofpropagation)togetthesessionidentifierassignedbyPHP.
ThisapproachisillustratedinFigure4-4.
Toaddressthisweakness,ithelpstounderstandthescopeoftheproblem.
Sessionfixationismerelyastepping-stone—thepurposeoftheattackistogetasessioniden-tifierthatcanbeusedtohijackasession.
Thisismostusefulwhenthesessionbeinghijackedhasahigherlevelofprivilegethantheattackercanobtainthroughlegiti-matemeans.
Thislevelofprivilegecanbeassimpleasbeingloggedin.
Ifthesessionidentifierisregeneratedeverytimethereisachangeinthelevelofprivi-lege,theriskofsessionfixationispracticallyeliminated:,ch04.
847Page46Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
SessionFixation|47Idonotrecommendregeneratingthesessionidentifieroneverypage.
Whilethisseemslikeasecureapproach—anditis—itprovidesnomoreprotectionthanregeneratingthesessionidentifierwheneverthereisachangeinthelevelofprivilege.
Moreimportantly,itcanadverselyaffectyourlegitimateusers,especiallyifthesessionidenti-fierisbeingpropagatedintheURL.
Ausermightusethebrowser'shistorymechanismtoreturntoapreviouspage,andthelinksonthatpagewillreferenceasessionidentifierthatnolongerexists.
Ifyouregeneratethesessionidentifieronlywhenthereisachangeinthelevelofprivilege,thesamesituationispossible,butauserwhoreturnstoapagepriortothechangeinthelevelofprivilegeislesslikelytobesurprisedbyalossofsession,andthissituationisalsolesscommon.
Figure4-4.
AsessionfixationattackcanfirstinitializethesessionAttacker1target.
example.
orgHTTP/1.
1200OKSet-Cookie:PHPSESSID=412e11d52Victim4example.
org53AttackerAttackerupdatescontenttoincludealinkwithanembeddedPHPSESSIDtarget.
example.
org6GET/login.
phpPHPSESSID=412e11d5HTTP/1.
1Host:target.
example.
org,ch04.
847Page47Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
48|Chapter4:SessionsandCookiesSessionHijackingThemostcommonsessionattackissessionhijacking.
Thisreferstoanymethodthatanattackercanusetoaccessanotheruser'ssession.
Thefirststepforanyattackeristoobtainavalidsessionidentifier,andthereforethesecrecyofthesessionidentifierisparamount.
Theprevioussectionsonexposureandfixationcanhelpyoutokeepthesessionidentifierasharedsecretbetweentheserverandalegitimateuser.
TheprincipleofDefenseinDepth(describedinChapter1)canbeappliedtoses-sions—someminorsafeguardscanoffersomeprotectionintheunfortunatecasethatthesessionidentifierisknownbyanattacker.
Asasecurity-consciousdeveloper,yourgoalistocomplicateimpersonation.
Everyobstacle,howeverminor,offerssomeprotection.
Thekeytocomplicatingimpersonationistostrengthenidentification.
Thesessionidentifieristheprimarymeansofidentification,andyouwanttoselectotherdatathatyoucanusetoaugmentthis.
TheonlydatayouhaveavailableisthedatawithineachHTTPrequest:GET/HTTP/1.
1Host:example.
orgUser-Agent:Firefox/1.
0Accept:text/html,image/png,image/jpeg,image/gif,*/*Cookie:PHPSESSID=1234Youwanttorecognizeconsistencyinrequestsandtreatanyinconsistentbehaviorwithsuspicion.
Forexample,whiletheUser-Agentheaderisoptional,clientsthatsenditdonotoftenalteritsvalue.
Iftheuserwithasessionidentifierof1234hasbeenusingMozillaFirefoxconsistentlysinceloggingin,asuddenswitchtoInternetExplorershouldbetreatedwithsuspicion.
Forexample,promptingforthepass-wordisaneffectivewaytomitigatetheriskwithminimalimpacttoyourlegitimateusersinthecaseofafalsealarm.
YoucancheckforUser-Agentconsistencyasfollows:,ch04.
847Page48Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
SessionHijacking|49IhaveobservedthatsomeversionsofInternetExplorersendadiffer-entAcceptheaderdependinguponwhethertheuserrefreshesthebrowser,soAcceptshouldnotberelieduponforconsistency.
RequiringaconsistentUser-Agenthelps,butifthesessionidentifierisbeingpropa-gatedinacookie(therecommendedapproach),itisreasonabletoassumethat,ifanattackercancapturethesessionidentifier,hecanmostlikelycapturethevalueofallotherHTTPheadersaswell.
Becausecookiedisclosuretypicallyinvolvesabrowservulnerabilityorcross-sitescripting,thevictimhasmostlikelyvisitedtheattacker'swebsite,disclosingallheaders.
AllanattackermustdoisreproduceallofthesetoavoidanyconsistencycheckthatusesHTTPheaders.
AbetterapproachistopropagateatokenintheURL—somethingthatcanbecon-sideredasecond(albeitmuchweaker)formofidentification.
Thispropagationtakessomework—thereisnofeatureofPHPthatdoesitforyou.
Forexample,assumingthetokenisstoredin$token,allinternallinksinyourapplicationneedtoincludeit:">ClickHereTomakepropagationabiteasiertomanage,youmightconsiderkeep-ingtheentirequerystringinavariable.
Youcanappendthisvariabletoallofyourlinks,whichmakesiteasytorefactoryourcodelater,evenifyoudon'timplementthistechniqueinitially.
Thetokenneedstobesomethingthatcannotbepredicted,evenundertheconditionthattheattackerknowsalloftheHTTPheadersthatthevictim'sbrowsertypicallysends.
Onewaytoachievethisistogeneratethetokenusingarandomstring:,ch04.
847Page49Friday,October14,200511:27AMThisistheTitleoftheBook,eMatterEditionCopyright2005O'Reilly&Associates,Inc.
Allrightsreserved.
50|Chapter4:SessionsandCookiesWhenyouusearandomstring(SHIFLETTinthisexample),predictionisimpractical.
Inthiscase,capturingthetokeniseasierthanpredictingit,andbypropagatingthetokenintheURLandthesessionidentifierinacookie,multipleattacksareneededtocaptureboth.
Theexceptioniswhentheattackercanobservethevictim'srawHTTPrequestsastheyaresenttoyourapplication,becausethisdisclosesevery-thing.
Thistypeofattackismoredifficult(andthereforelesslikely),anditcanbemitigatedbyusingSSL.
SomeexpertswarnagainstrelyingontheconsistencyofUser-Agent.
TheconcernisthatanHTTPproxyinaclustercanmodifyUser-Agentinconsistentlywithotherproxiesinthesamecluster.
IfyoudonotwanttodependonUser-Agentconsistency,youcangeneratearandomtoken:Thisapproachisslightlyweaker,butitismuchmorereliable.
Bothmethodsprovideastrongdefenseagainstsessionhijacking.
Theappropriatebalancebetweensecurityandreliabilityisuptoyou.
,ch04.
847Page50Friday,October14,200511:27AM

博鳌云¥799/月,香港110Mbps(含10M CN2)大带宽独立服务器/E3/8G内存/240G/500G SSD或1T HDD

博鳌云是一家以海外互联网基础业务为主的高新技术企业,运营全球高品质数据中心业务。自2008年开始为用户提供服务,距今11年,在国人商家中来说非常老牌。致力于为中国用户提供域名注册(国外接口)、免费虚拟主机、香港虚拟主机、VPS云主机和香港、台湾、马来西亚等地服务器租用服务,各类网络应用解決方案等领域的专业网络数据服务。商家支持支付宝、微信、银行转账等付款方式。目前香港有一款特价独立服务器正在促销,...

CloudCone,美国洛杉矶独立服务器特价优惠,美国洛杉矶MC机房,100Mbps带宽不限流量,可选G口,E3-1270 v2处理器32G内存1Gbps带宽,69美元/月

今天CloudCone发布了最新的消息,推送了几款特价独立服务器/杜甫产品,美国洛杉矶MC机房,分配100Mbps带宽不限流量,可以选择G口限制流量计划方案,存储分配的比较大,选择HDD硬盘的话2TB起,MC机房到大陆地区线路还不错,有需要美国特价独立服务器的朋友可以关注一下。CloudCone怎么样?CloudCone服务器好不好?CloudCone值不值得购买?CloudCone是一家成立于2...

WHloud Date鲸云数据($9.00/月), 韩国,日本,香港

WHloud Date(鲸云数据),原做大数据和软件开发的团队,现在转变成云计算服务,面对海内外用户提供中国大陆,韩国,日本,香港等多个地方节点服务。24*7小时的在线支持,较为全面的虚拟化构架以及全方面的技术支持!官方网站:https://www.whloud.com/WHloud Date 韩国BGP云主机少量补货随时可以开通,随时可以用,两小时内提交退款,可在工作日期间全额原路返回!支持pa...

phpwind为你推荐
支持ipadaspweb服务器asp网站挂上服务器,详细步骤德国iphone禁售令德国买iPhone现在多少钱?中国企业信息网中国企业网怎么样cuteftp什么是 CuteFtp Flashfxp Leapftp FlashGetmy.qq.commy.qq.com,QQ用户上不去?美要求解锁iPhoneiPhone连接Mac的时候出现提示需要解锁iPhoneyixingjia合家欢是一种什么东西?温州商标注册温州注册公司在哪里注册刚刚网刚刚在网上认识了一个女孩子,不是很了解她,就跟她表白了。
ip查域名 域名服务器上存放着internet主机的 樊云 息壤主机 vps.net webhosting 空间打开慢 2017年万圣节 服务器维护方案 亚马逊香港官网 免费cdn 如何注册阿里云邮箱 双线asp空间 中国电信测速器 便宜空间 阿里云邮箱登陆地址 宿迁服务器 apnic fatcow tracert 更多