!'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
racknerd怎么样?racknerd商家最近促销三款美国便宜vps,最低只需要9.49美元,可以选择美国圣何塞、西雅图、纽约和芝加哥机房。RackNerd是一家成立于2019年的美国高性价比服务器商家,主要从事美国和荷兰数据中心的便宜vps、独立服务器销售!支持中文工单、支持支付宝和微信以及PayPal付款购买!点击直达:racknerd官方网站INTEL系列可选机房:加利福尼亚州圣何塞、芝加...
Advinservers,国外商家,公司位于新泽西州,似乎刚刚新成立不久,主要提供美国和欧洲地区VPS和独立服务器业务等。现在有几款产品优惠,高达7.5TB的存储VPS和高达3.5TBDDoS保护的美国纽约高防服务器,性价比非常不错,有兴趣的可以关注一下,并且支持Paypal付款。官方网站点击直达官方网站促销产品第一款VPS为预购,预计8月1日交付。CPU为英特尔至强 CPU(X 或 E5)。官方...
无忧云怎么样?无忧云是一家成立于2017年的老牌商家旗下的服务器销售品牌,现由深圳市云上无忧网络科技有限公司运营,是正规持证IDC/ISP/IRCS商家,主要销售国内、中国香港、国外服务器产品,线路有腾讯云国外线路、自营香港CN2线路等,都是中国大陆直连线路,非常适合免备案建站业务需求和各种负载较高的项目,同时国内服务器也有多个BGP以及高防节点,目前商家开启了夏日清凉补贴活动,商家的机器还是非常...
phpwind为你推荐
苹果appstore宕机苹果appstore打不开怎么办波音737起飞爆胎客机起飞的时候时速是多少?申请支付宝账户如何申请支付宝账户重庆电信dns重庆电信 路由器连接另一个电脑,本地连接的IP是多少,?DNS首选,备用 服务器是多少?银花珠树晓来看用黄皮比喻心酸的诗句申请400电话电话是什么电话啊?怎么申请400电话400呢?具体收费价格是什么?discuz伪静态Discuz! X3.0 到底能不能伪静态?门户怎么伪静态?网站后台密码破解网站后台管理密码忘记了怎么破解啊高手进来.地址栏图标地址栏中网址前面的图标代表着什么?艾泰科技艾泰的品牌介绍
外国虚拟主机 域名邮箱 备案域名查询 美国主机排名 香港bgp机房 樊云 正版win8.1升级win10 isp服务商 傲盾官网 重庆双线服务器托管 无限流量 免费邮件服务器 备案空间 电信网络测速器 免费个人主页 实惠 阿里云邮箱登陆 ssl加速 存储服务器 shuangcheng 更多