Microsoft Windows – ‘USP10!SubstituteNtoM’ Uniscribe Font Processing Out-of-Bounds Memory Read
Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1200 We have encountered a crash in the Windows Uniscribe user-mode library, in the USP10!SubstituteNtoM function, while trying to display text using a corrupted TTF font file: --- (69c.164): Access violation - code c0000005 (first chance) First chance exceptions are reported before any exception handling. This exception may be expected and handled. eax=035fc256 ebx=00000000 ecx=035fc256 edx=00000019 esi=035cc1d0 edi=00000001 eip=7750a774 esp=0014eb38 ebp=0014eb64 iopl=0 nv up ei pl nz na pe nc cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00010206 USP10!SubstituteNtoM+0x2c4: 7750a774 668b08 mov cx,word ptr [eax] ds:0023:035fc256=???? 0:000> kb # ChildEBP RetAddr Args to Child 00 0014eb64 7750994d 0014ef40 0014ef64 035fc256 USP10!SubstituteNtoM+0x2c4 01 0014eba8 7750142a 0014ef40 0014ef64 0014ee54 USP10!otlMultiSubstLookup::apply+0x10d 02 0014ec10 775039f1 00000000 0014ef40 00001c3a USP10!ApplyLookup+0x1aa 03 0014ee14 774fefcf 42555347 0014ef7c 0014ef40 USP10!ApplyFeatures+0x481 04 0014ee60 774ff920 00000000 035f3ffe 035f3c90 USP10!SubstituteOtlGlyphs+0x1bf 05 0014ee9c 774f1500 0014ef18 0014ef50 0014ef7c USP10!SubstituteOtlChars+0x220 06 0014f118 774e55da 0014f224 0014f250 0014f238 USP10!HebrewEngineGetGlyphs+0x690 07 0014f1d8 774e273f 0014f224 0014f250 0014f238 USP10!ShapingGetGlyphs+0x36a 08 0014f2c4 774b5c6f a30105a2 035c6124 035c6318 USP10!ShlShape+0x2ef 09 0014f308 774c174a a30105a2 035c6124 035c6318 USP10!ScriptShape+0x15f 0a 0014f368 774c2bd4 00000000 00000000 0014f3e8 USP10!RenderItemNoFallback+0xfa 0b 0014f394 774c2e62 00000000 00000000 0014f3e8 USP10!RenderItemWithFallback+0x104 0c 0014f3b8 774c43f9 00000000 0014f3e8 035c6124 USP10!RenderItem+0x22 0d 0014f3fc 774b7a04 000004a0 00000400 a30105a2 USP10!ScriptStringAnalyzeGlyphs+0x1e9 0e 0014f414 760a1736 a30105a2 035c6040 0000000a USP10!ScriptStringAnalyse+0x284 0f 0014f460 760a18c1 a30105a2 0014f8e4 0000000a LPK!LpkStringAnalyse+0xe5 10 0014f55c 760a17b4 a30105a2 00000000 00000000 LPK!LpkCharsetDraw+0x332 11 0014f590 77df56a9 a30105a2 00000000 00000000 LPK!LpkDrawTextEx+0x40 12 0014f5d0 77df5a64 a30105a2 00000728 00000000 USER32!DT_DrawStr+0x13c 13 0014f61c 77df580f a30105a2 0014f8e4 0014f8f8 USER32!DT_GetLineBreak+0x78 14 0014f6c8 77df5882 a30105a2 00000000 0000000a USER32!DrawTextExWorker+0x250 15 0014f6ec 77df5b68 a30105a2 0014f8e4 ffffffff USER32!DrawTextExW+0x1e [...] --- The issue reproduces on Windows 7, and could be potentially used to disclose sensitive data from the process heap. 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. Attached are 2 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/42236.zip |