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Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1198

We have encountered a crash in the Windows Uniscribe user-mode library, in the memmove() function called by USP10!MergeLigRecords, while trying to display text using a corrupted font file:

---
(4e0.6dc): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000001 ebx=00000036 ecx=000023af edx=00000003 esi=03624337 edi=0362436d
eip=76e1026a esp=003cefd8 ebp=003cefe0 iopl=0         nv up ei pl nz ac pe nc
cs=001b  ss=0023  ds=0023  es=0023  fs=003b  gs=0000             efl=00010216
msvcrt!memmove+0x224:
76e1026a 8a4603          mov     al,byte ptr [esi+3]        ds:0023:0362433a=??
0:000> kb
 # ChildEBP RetAddr  Args to Child              
00 003cefe0 774c772d 03621fc1 03621f8b 000023b0 msvcrt!memmove+0x224
01 003ceffc 774c75c3 03615fd0 036159d0 003cf098 USP10!MergeLigRecords+0x3d
02 003cf05c 774c7124 0000001a 035b3d88 035bffa8 USP10!LoadTTOArabicShapeTables+0x3f3
03 003cf070 774cc734 2e0105bd 035b3d88 035a6124 USP10!LoadArabicShapeTables+0xd4
04 003cf08c 774ba5a0 2e0105bd 036157d0 0000001a USP10!ArabicLoadTbl+0xd4
05 003cf0b4 774ba692 035a6124 2e0105bd 0000001a USP10!UpdateCache+0xb0
06 003cf0c8 774c15fd 2e0105bd 035a6000 774c16ab USP10!ScriptCheckCache+0x62
07 003cf0d4 774c16ab 00000001 00000001 00000000 USP10!GetShapeFunction+0xd
08 003cf10c 774c2bd4 00000001 00000004 003cf18c USP10!RenderItemNoFallback+0x5b
09 003cf138 774c2e62 00000001 00000004 003cf18c USP10!RenderItemWithFallback+0x104
0a 003cf15c 774c43f9 00000004 003cf18c 035a6124 USP10!RenderItem+0x22
0b 003cf1a0 774b7a04 000004a0 00000400 2e0105bd USP10!ScriptStringAnalyzeGlyphs+0x1e9
0c 003cf1b8 760a1736 2e0105bd 035a6040 0000000a USP10!ScriptStringAnalyse+0x284
0d 003cf204 760a18c1 2e0105bd 003cf688 0000000a LPK!LpkStringAnalyse+0xe5
0e 003cf300 760a17b4 2e0105bd 00000000 00000000 LPK!LpkCharsetDraw+0x332
0f 003cf334 77df56a9 2e0105bd 00000000 00000000 LPK!LpkDrawTextEx+0x40
10 003cf374 77df5a64 2e0105bd 00000048 00000000 USER32!DT_DrawStr+0x13c
11 003cf3c0 77df580f 2e0105bd 003cf688 003cf69c USER32!DT_GetLineBreak+0x78
12 003cf46c 77df5882 2e0105bd 00000000 0000000a USER32!DrawTextExWorker+0x250
13 003cf490 77df5b68 2e0105bd 003cf688 ffffffff USER32!DrawTextExW+0x1e
14 003cf4c4 000e6c3a 2e0105bd 003cf688 ffffffff USER32!DrawTextW+0x4d
[...]
0:000> db poi(ebp+8)
03621fc1  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fd1  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fe1  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621ff1  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 d0 d0 d0 d0 ??  ...............?
03622001  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
03622011  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
03622021  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
03622031  ?? ?? ?? ?? ?? ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  ????????????????
0:000> db poi(ebp+c)
03621f8b  00 b5 00 b7 00 b9 00 bb-00 bd 00 bf 00 c3 00 c5  ................
03621f9b  00 c9 00 cb 00 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fab  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fbb  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fcb  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621fdb  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621feb  c0 c0 c0 c0 c0 c0 c0 c0-c0 c0 c0 c0 c0 c0 c0 c0  ................
03621ffb  c0 d0 d0 d0 d0 ?? ?? ??-?? ?? ?? ?? ?? ?? ?? ??  .....???????????
0:000> dd esi
03624337  ???????? ???????? ???????? ????????
03624347  ???????? ???????? ???????? ????????
03624357  ???????? ???????? ???????? ????????
03624367  ???????? ???????? ???????? ????????
03624377  ???????? ???????? ???????? ????????
03624387  ???????? ???????? ???????? ????????
03624397  ???????? ???????? ???????? ????????
036243a7  ???????? ???????? ???????? ????????
0:000> dd edi
0362436d  ???????? ???????? ???????? ????????
0362437d  ???????? ???????? ???????? ????????
0362438d  ???????? ???????? ???????? ????????
0362439d  ???????? ???????? ???????? ????????
036243ad  ???????? ???????? ???????? ????????
036243bd  ???????? ???????? ???????? ????????
036243cd  ???????? ???????? ???????? ????????
036243dd  ???????? ???????? ???????? ????????
---

The issue reproduces on Windows 7. It is easiest to reproduce with PageHeap enabled, but it is also possible to observe a crash in a default system configuration. In order to reproduce the problem with the provided samples, it might be necessary to use a custom program which displays all of the font's glyphs at various point sizes.

It's worth noting that the crash is almost identical to the one reported in  Issue #1026 , which was supposedly fixed as CVE-2017-0087 in the MS17-011 bulletin. The number of times we have encountered this crash while fuzzing the patched version of USP10.DLL might suggest that the fix was incomplete (or alternatively, that there is a separate bug which causes a crash in the same code location).

Attached are 6 proof of concept malformed font files which trigger the crash.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/42234.zip