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Oct 20, 2020

README.md

CVE-2020-16947

This vulnerability occurs in Outlook 2019 (16.0.13231.20262) installed on Windows 10 1909 x64

TLDR;

I found this bug using winafl fuzzer. This bug occured when parsing html contents. if attacker successfully executes this exploit, it can lead to remote command execution.

Details

0:000> r
rax=0000000000000000 rbx=0000021c99ce9eb0 rcx=0000021c99ce9eb0
rdx=00000046c07f8a30 rsi=0000021cc85ac000 rdi=00000000ffffe000
rip=00007ffe69012f5b rsp=00000046c07f89f0 rbp=00000046c07f8a69
 r8=00000046c07f8a28  r9=0000000000000041 r10=00007de1cf5e3124
r11=0000000000000000 r12=00000046c07f8b00 r13=0000021c99ce9f1c
r14=0000000000000041 r15=00000000000003b5
iopl=0         nv up ei pl zr na po nc
cs=0033  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010246
OLMAPI32!HrGetMessageClassFromContentClassW+0xf80b:
00007ffe`69012f5b 448836          mov     byte ptr [rsi],r14b ds:0000021c`c85ac000=??
0:000> d rsi - 10
0000021c`c85abff0  ff fd ff fd ff fd ff fd-ff fd ff fd ff fd ff 41  ...............A
0000021c`c85ac000  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac010  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac020  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac030  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac040  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac050  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0000021c`c85ac060  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0:000> !heap -p -a rsi
    address 0000021cc85ac000 found in
    _DPH_HEAP_ROOT @ 21ce0331000
    in busy allocation (  DPH_HEAP_BLOCK:         UserAddr         UserSize -         VirtAddr         VirtSize)
                             21ccb3eb000:      21cc85a7ff0             4010 -      21cc85a7000             6000
    00007ffea238825b ntdll!RtlDebugAllocateHeap+0x000000000000003b
    00007ffea22a9745 ntdll!RtlpAllocateHeap+0x00000000000000f5
    00007ffea22a73d4 ntdll!RtlpAllocateHeapInternal+0x00000000000006d4
    00007ffe68c8777d OLMAPI32!MAPIAllocateBuffer+0x00000000000000cd
    00007ffe69012a35 OLMAPI32!HrGetMessageClassFromContentClassW+0x000000000000f2e5
    00007ffe69015d34 OLMAPI32!HrTextFromCompressedRTFStreamEx+0x00000000000023d4
    00007ffe68dcc776 OLMAPI32!RTFSyncCpid+0x0000000000000156
    00007ffe7c3eb532 exsec32!HrExsec32Initialize+0x0000000000005372
    00007ffe7c3e5631 exsec32+0x0000000000005631
    00007ffe68dccc76 OLMAPI32!RTFSyncCpid+0x0000000000000656
    00007ffe68de2ab4 OLMAPI32!HrCreateMHTMLConverter+0x0000000000002634
    00007ffe68dd21a7 OLMAPI32!MlangIsConvertible+0x0000000000004a07
    00007ffe68de299d OLMAPI32!HrCreateMHTMLConverter+0x000000000000251d
    00007ffe7c42748f exsec32!DllUnregisterServer+0x00000000000002bf
    00007ffe7c3eb418 exsec32!HrExsec32Initialize+0x0000000000005258
    00007ffe7c3e5631 exsec32+0x0000000000005631
    00007ffe551703d9 OUTLMIME!MimeOleInetDateToFileTime+0x0000000000025539
    00007ffe551709f9 OUTLMIME!MimeOleInetDateToFileTime+0x0000000000025b59
    00007ffe55174dec OUTLMIME!MimeOleInetDateToFileTime+0x0000000000029f4c
    00007ffe55175279 OUTLMIME!MimeOleInetDateToFileTime+0x000000000002a3d9
    00007ffe55174ebe OUTLMIME!MimeOleInetDateToFileTime+0x000000000002a01e
    00007ffe7c41a8fc exsec32!HrMaxAlgStrength+0x0000000000004cac
    00007ffe7c3eb017 exsec32!HrExsec32Initialize+0x0000000000004e57
    00007ffe7c3ebf23 exsec32!HrExsec32Initialize+0x0000000000005d63
    00007ffe49ac9f47 mso98win32client!Ordinal3621+0x00000000000000e7
    00007ffe49ac9ecd mso98win32client!Ordinal3621+0x000000000000006d
    00007ff7afc43f79 outlook!FEnableAMapProgress+0x000000000002f099
    00007ff7afdb638d outlook!UpdateSharingAccounts+0x000000000007031d
    00007ff7afdc3d85 outlook!IsOutlookOutsideWinMain+0x0000000000003af5
    00007ff7afcf7727 outlook!HrGetDelegatorInfoSync+0x00000000000016e7
    00007ff7afd2a2b0 outlook!GetOutlookSafeModeState+0x000000000000bd00
    00007ff7afd2a14b outlook!GetOutlookSafeModeState+0x000000000000bb9b

When copying strings out of the ascii range among html contents, the corresponding string is replaced with 0xfffd. As a result, the size of the copied string doubles, so despite the same size of the src buffer and dst buffer, buffer overflow occurs.

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PoC of CVE-2020-16947 (Microsoft Outlook RCE vulnerablility)

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