the mummy 2018 - microsoft summons back ugly …...“fragmentation considered vulnerable”, gilad,...

TheMummy2018- MicrosoftSummonsBackUglyAttacksFromThePast

WhoamI

• RanMenscher– Israel

• IndependentSoftwareResearcher– ReverseEngineering

• OSinternals,Embedded,Applications…

• Past:VPResearch,XMCyber

– Vulnerabilities• YesJ

I’mgoingtotellyouabout

• AnunusualbuginWindowsIPstack

• FragmentationandIPIDrandomization– Overview,pastattacks– Thebug(CVE-2018-8493)– Exploitation

• Othercoolconsequences

FragmentationandReassembly

UndeniablyCursed

UndeniablyCursed• Reassemblysensitive toresourceexhaustion/otherDoS

UndeniablyCursed• Reassemblysensitive toresourceexhaustion/otherDoSMore

fragmentscomingup You’re

kidding…

UndeniablyCursed• Reassemblysensitive toresourceexhaustion/otherDoS• LotsofattacksurfacetoevadeIDS

Undeniablycursed• Reassemblysensitive toresourceexhaustion/otherDoS• LotsofattacksurfacetoevadeIDS

(source:onlinepresentationbyTobiasRenwick)

UndeniablyCursed• Reassemblysensitive toresourceexhaustion/otherDoS• LotsofattacksurfacetoevadeIDS• MostImplementations:IPIDsasGlobalCounter

CurseofGlobalCounter• DeNATing• IdleScanning

CurseofGlobalCounter• DeNATing• IdleScanning• Blindpacketinjection(Zalewski 03)

CurseofGlobalCounter• DeNATing• IdleScanning• Blindpacketinjection(Zalewski 03)

Valid DST Port

CurseofGlobalCounter• DeNATing• IdleScanning• Blindpacketinjection(Zalewski 03)• Trafficinterception byNAT/Tunnel(Gilad,Herzberg11)

CurseofGlobalCounter• DeNATing• IdleScanning• Blindpacketinjection(Zalewski 03)• Trafficinterception byNAT/Tunnel(Gilad,Herzberg11)

“Fragmentation Considered Vulnerable”, Gilad, Herzberg2011

Sothevendorswerequicktosealthecurse

Sothevendorswerequicktosealthecurse• GlobalCounterinWindowsuntil2012(perinterface)• windows8• DifferentIPIDperIPpath• Andtheyweresafeandhappy

For8.1,a“major”refactorhadtakenplaceforIPIDs:Mostprominentchanges:• Afunctionisn’tinline’d anymore– (but thatcouldbethecompiler)

• Anarraywaschangedtoapointer

• Whydidtheychangeit?

IPIDGENERATION

• IsaboutIP PATH

• IsaboutIP PATH

identification = base + increment

• IsaboutIP PATH


Random4bytes(init @boot)⨁

hash(key,IPPATH)

• IsaboutIP PATH


Random4bytes(init @boot)⨁

hash(key,IPPATH)increments[ hash(key,IPPATH)]

Oops

• Allocate0x8000• Initialize8… bytes• Sizeof(int *)• Mostlyzeros

Oops

• 5

• IsaboutIP PATH


Random4bytes (init @boot)⨁

hash(key,IPPATH)increments[ hash(key,IPPATH)]

• key is40randombytes• hash isaToeplitz hash(RSS)• Toeplitz matrices

Key

00000 45678 67456 7867420384 09234 93759 1298747823 28002 23532 7593066783 48759 28465 93732

00000 55080 90366 9829588998 33569 56486 1716689406 29886 53232 4467887289 20230 91489 43798, …

• key is40randombytes• hash isaToeplitz hash• Toeplitz matrices

INPUT2 F 3

00000 45678 67456 7867420384 09234 93759 1298747823 28002 23532 7593066783 48759 28465 93732

00000 55080 90366 9829588998 33569 56486 1716689406 29886 53232 4467887289 20230 91489 43798,

…

Hash=tbl1[0x2] ⨁ tbl2[0xF]⨁ …

00000 45678 67456 7867420384 09234 93759 1298747823 28002 23532 7593066783 48759 28465 93732,

• Nibblesofinput,thatareXOR8ofeachother–TheirhashesareXOR key[i]ofeachother!


• Nibblesofinput,thatareXOR8ofeachother–TheirhashesareXORkey[i]ofeachother!


Inputsthatdifferonlybyanibblewilloutputacell’scontent!


• Hash(10.0.0.1,10.0.0.2) =1234⨁ 5453⨁ … ⨁ 0• Hash(0x80|10.0.0.1,10.0.0.2)=1234⨁ 5453⨁ …⨁ key[i]




• id(10.0.0.1,10.0.0.2) =1234⨁ 5453⨁ … ⨁ 0 ⨁ secret• id(0x80|10.0.0.1,10.0.0.2)=1234⨁ 5453⨁ … ⨁ key[i] ⨁ secret




• id(10.0.0.1,10.0.0.2) =1234⨁ 5453⨁ … ⨁ 0 ⨁ secret• id(0x80|10.0.0.1,10.0.0.2)=1234⨁ 5453⨁ … ⨁ key[i] ⨁ secret

ID1⨁ ID2=key[i]

ATTACK(keyrecovery):• GettwosamplesofIPIDs• ForIPPATHs thatdifferbyanibble.XOR8ofeachother.• Key[0]=ID1 ^ID2 (ifwehitincrement=0)• Repeatuntilconfidentofkey[0]• Repeatforotherkeyparts

identification1 = key[i]⨁ identification2

identification1 = key[i]⨁ identification2

• Butifincrement≠0• Wecandeducecontentfromthetable(=uninitializedmem)

Ifincrement1 ==0 Ifincrement2 ==0

ATTACK(readingkernelmem)• ChooseIPIDforIPPATHsknowntohaveincrement=0• UserecoveredkeytoinitializeToeplitz matrixvalues• GetIPIDsforIPPATHsdifferingbyanibblefromchosenIPPATH• CalculateexpectedIPIDsaccordingtomatrix• Sample – Expected =Tablecontent=uninitializedmem

PredictingIPIDs• Whenincrement=0,predictionispractical• Workssimilarlytothememoryread• Problemreducedtoassessing#ofpacketssent

TakeAways

• DontFragment (DF)isnotjustanIPflag.it’sgoodadvice.

• Yes,Coderswhorefactorworkingcodearegraverobbers.

• Ifyoumixperformanceandsecurity,asimplebugwillbringyoudown.

Questions?

[email protected]:@menscherr

the mummy 2018 - microsoft summons back ugly …...“fragmentation considered vulnerable”, gilad,...

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