We have observed the following access violation exception in the latest version of Adobe Acrobat Reader DC for Windows, when opening a malformed PDF file:

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(50a8.4100): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=ff3a0000 ebx=00003f11 ecx=00002000 edx=00000001 esi=0077bdfc edi=8c9e5000
eip=64b40fb5 esp=0077bdc0 ebp=0077be18 iopl=0         nv up ei pl nz na pe nc
cs=0023  ss=002b  ds=002b  es=002b  fs=0053  gs=002b             efl=00010206
CoolType!CTCleanup+0x26ba7:
64b40fb5 894704          mov     dword ptr [edi+4],eax ds:002b:8c9e5004=????????

0:000> kb
 # ChildEBP RetAddr  Args to Child              
WARNING: Stack unwind information not available. Following frames may be wrong.
00 0077be18 64b05405 64d48440 8605cdcc 00000001 CoolType!CTCleanup+0x26ba7
01 0077be34 64b04548 64d48284 27618cb0 0077c5e8 CoolType!CTInit+0x6267e
02 0077be44 64b10fa7 0077be94 64d50130 0077be88 CoolType!CTInit+0x617c1
03 0077c5e8 64b107bf 8605cdcc 0077c60c 0077c6a8 CoolType!CTInit+0x6e220
04 0077c6a0 64b10736 8d3a8ff8 0077c6ec 8c3ccfa8 CoolType!CTInit+0x6da38
05 0077c6b4 64b106c3 8605cd70 0077c6ec 8c3ccfa8 CoolType!CTInit+0x6d9af
06 0077c6c8 64b1051c 8605cd70 0077c6ec 8c3ccfa8 CoolType!CTInit+0x6d93c
07 0077c70c 64b10398 0077c7ec 5f8bc1ec 0077c7b0 CoolType!CTInit+0x6d795
08 0077c738 64b1032b 0077c7ec 5f8bc1b4 0077c7b0 CoolType!CTInit+0x6d611
09 0077c760 64b10208 8c3c8ff0 0077c7ec 5f8bc144 CoolType!CTInit+0x6d5a4
0a 0077c790 64adb3c0 8c3c8ff0 0077c7ec 5f8bcf58 CoolType!CTInit+0x6d481
0b 0077c98c 64ac036d 8605cd70 0077c9c4 5f8bcf3c CoolType!CTInit+0x38639
0c 0077c9e8 64ac1c20 64d31918 00000001 00000000 CoolType!CTInit+0x1d5e6
0d 0077ca18 64ac5eff 8605cd70 64d31918 00000001 CoolType!CTInit+0x1ee99
0e 0077ca54 64ac036d 8605cd70 0077ca8c 5f8bcc64 CoolType!CTInit+0x23178
0f 0077cab0 64ac1c20 64d319d0 00000001 00000000 CoolType!CTInit+0x1d5e6
10 0077cae0 64ac2229 8605cd70 64d319d0 00000001 CoolType!CTInit+0x1ee99
11 0077cb14 64ac5c4d 64d319d0 92280fc8 00000004 CoolType!CTInit+0x1f4a2
12 0077cb4c 64ac32ba 8ce40fc0 5f8bd684 0077d138 CoolType!CTInit+0x22ec6
13 0077d050 64ac31b3 8605cd70 8ce40fc0 0077d0b0 CoolType!CTInit+0x20533
14 0077d088 64ac2ef7 8605cd70 8ce40fc0 0077d0b0 CoolType!CTInit+0x2042c
15 0077d0cc 64ac2d85 0077d1a0 00000000 8605cd00 CoolType!CTInit+0x20170
16 0077d10c 64acdad7 0077d1a0 8ce40fc0 00000000 CoolType!CTInit+0x1fffe
17 0077d168 64acd96f 0077d1a0 8ce40fc0 91bbb002 CoolType!CTInit+0x2ad50
18 0077d1b8 123bf455 8cae2f08 64d32280 91bbb002 CoolType!CTInit+0x2abe8
19 0077d1dc 123be4e2 91bbb002 00000007 00000000 AcroRd32!DllCanUnloadNow+0x176495
1a 0077e544 123ba692 0077e690 8b972f68 00000004 AcroRd32!DllCanUnloadNow+0x175522
1b 0077e72c 123ba2fe 0077e740 91b7ea98 00000000 AcroRd32!DllCanUnloadNow+0x1716d2
1c 0077e780 123b655c 0077e810 8b972f68 00000000 AcroRd32!DllCanUnloadNow+0x17133e
1d 0077e838 123a93ed b7e1e317 78d62f78 00000000 AcroRd32!DllCanUnloadNow+0x16d59c
1e 0077e918 123a81e8 00000001 00000000 00000000 AcroRd32!DllCanUnloadNow+0x16042d
1f 0077e964 1239b383 78d62f78 00000000 00000000 AcroRd32!DllCanUnloadNow+0x15f228
20 0077ead8 1239ac97 9096fdbc 00000001 870c2ef8 AcroRd32!DllCanUnloadNow+0x1523c3
21 0077eb40 12398590 b7e1e1cf 96476e74 870c2ef8 AcroRd32!DllCanUnloadNow+0x151cd7
22 0077ebc0 1239825a 870c2ef8 8de26f40 96476e44 AcroRd32!DllCanUnloadNow+0x14f5d0
23 0077ebfc 12416099 870c2ef8 8de26f40 96476e44 AcroRd32!DllCanUnloadNow+0x14f29a
24 0077ecd4 124157f9 8ae88fc8 00000000 8de26f40 AcroRd32!CTJPEGDecoderRelease+0x2b209
25 0077ed14 12415717 8ae88fc8 00000000 8de26f40 AcroRd32!CTJPEGDecoderRelease+0x2a969
26 0077ed4c 12415669 00000000 8de26f40 0077eecc AcroRd32!CTJPEGDecoderRelease+0x2a887
27 0077ed68 124151ec 8de26f40 0077eecc 0077eee4 AcroRd32!CTJPEGDecoderRelease+0x2a7d9
28 0077ef30 12414a8c 00000009 00000000 ffffffff AcroRd32!CTJPEGDecoderRelease+0x2a35c
29 0077f150 124147d4 124147a0 8991cf90 0077f1a8 AcroRd32!CTJPEGDecoderRelease+0x29bfc
2a 0077f160 1226ed79 8d2061b8 b7e1fba7 8b612ff8 AcroRd32!CTJPEGDecoderRelease+0x29944
2b 0077f1a8 1226e83d 00000744 b7e1f817 15861fd8 AcroRd32!DllCanUnloadNow+0x25db9
2c 0077f218 1226e5d4 b7e1f84f 15861fd8 1226e560 AcroRd32!DllCanUnloadNow+0x2587d
2d 0077f240 12204709 000004d3 00000000 12204270 AcroRd32!DllCanUnloadNow+0x25614
2e 0077f25c 7460e0bb 00bc0f52 00000113 000004d3 AcroRd32!AcroWinMainSandbox+0x8909
2f 0077f288 74618849 12204270 00bc0f52 00000113 USER32!_InternalCallWinProc+0x2b
30 0077f2ac 7461b145 00000113 000004d3 00000000 USER32!InternalCallWinProc+0x20
31 0077f37c 746090dc 12204270 00000000 00000113 USER32!UserCallWinProcCheckWow+0x1be
32 0077f3e8 74608c20 1a382cee 0077f40c 1226da8b USER32!DispatchMessageWorker+0x4ac
33 0077f3f4 1226da8b 0077f428 1583ddd8 1583ddd8 USER32!DispatchMessageW+0x10
34 0077f40c 1226d81e 0077f428 b7e1fe8f 1583ddd8 AcroRd32!DllCanUnloadNow+0x24acb
35 0077f480 1226d6b4 b7e1feb7 1583ddd8 00000000 AcroRd32!DllCanUnloadNow+0x2485e
36 0077f4b8 121fc556 b7e1ff27 1458cff8 00000000 AcroRd32!DllCanUnloadNow+0x246f4
37 0077f528 121fbf81 121d0000 00af0000 1458cff8 AcroRd32!AcroWinMainSandbox+0x756
38 0077f948 00af783d 121d0000 00af0000 1458cff8 AcroRd32!AcroWinMainSandbox+0x181
39 0077fd14 00bffd2a 00af0000 00000000 0b6db3ba AcroRd32_exe+0x783d
3a 0077fd60 73cf8674 0041d000 73cf8650 be42f918 AcroRd32_exe!AcroRd32IsBrokerProcess+0x9940a
3b 0077fd74 77285e17 0041d000 11e63d34 00000000 KERNEL32!BaseThreadInitThunk+0x24
3c 0077fdbc 77285de7 ffffffff 772aadae 00000000 ntdll!__RtlUserThreadStart+0x2f
3d 0077fdcc 00000000 00af1390 0041d000 00000000 ntdll!_RtlUserThreadStart+0x1b
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Notes:

- Reproduces on Adobe Acrobat Reader DC (2019.012.20035) on Windows 10, with and without PageHeap enabled (more consistently with PageHeap, though).

- The crash occurs immediately after opening the PDF document, and is caused by an attempt to write data outside of an allocated buffer.

- It seems to be an off-by-one error, leading to an 8-byte overflow.

- Attached samples: poc.pdf (crashing file), original.pdf (original file).

- We have minimized the difference between the original and mutated files down to two bytes at offsets 0x3f523 and 0x40123 (0x65 => 0x75 and 0x15 => 0x05). These bytes reside inside of a Type 1 font stream.


Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/47274.zip