Headline
CVE-2021-21948: TALOS-2021-1376 || Cisco Talos Intelligence Group
A heap-based buffer overflow vulnerability exists in the readDatHeadVec functionality of AnyCubic Chitubox AnyCubic Plugin 1.0.0. A specially-crafted GF file can lead to a heap buffer overflow. An attacker can provide a malicious file to trigger this vulnerability.
Summary
A heap-based buffer overflow vulnerability exists in the readDatHeadVec functionality of AnyCubic Chitubox AnyCubic Plugin 1.0.0. A specially-crafted GF file can lead to a heap buffer overflow. An attacker can provide a malicious file to trigger this vulnerability.
Tested Versions
AnyCubic Chitubox AnyCubic Plugin 1.0.0
Chitubox Basic V1.8.1
Product URLs
https://www.chitubox.com
CVSSv3 Score
7.8 - CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CWE
CWE-122 - Heap-based Buffer Overflow
Details
The Chitubox AnyCubic plugin is used to convert the output of the Chitubox slicer (general format files) into the format expected by AnyCubic’s series of printers. These converted files are then used directly for all functionality provided by the printers.
A heap buffer overflow occurs within the GfFile::readDatHeadVec function seen below. The overflow occurs due to an integer overflow that occurs at [1] . This overflow is caused by using 32-bit registers instead of the extended 64-bit registers. The imul instruction will truncate the value during the multiplication, losing the most significant 32 bits. This calculated sized is used at [2] to allocate the correct size for the vector of GfDatHead_t. At [3] a very similar multiplication occurs, but uses a 64-bit register for the multiplication instead, thus eliminating the possibility of an overflow (since both values are loaded as 32-bit values). This new value calculated at [3] is used at [4] in the fread as a length of data to read into the buffer sized using the value calculated at [1] which is too small, resulting in a buffer overflow while reading the file contents into the buffer.
00006630 int64_t GfFile::readDatHeadVec(struct GfFile* this)
00006630 f30f1efa endbr64
00006634 53 push rbx {__saved_rbx}
00006635 488b9728010000 mov rdx, qword [rdi+0x128 {GfFile::gfDataHead.end}]
0000663c 4889fb mov rbx, rdi
0000663f 488b8f20010000 mov rcx, qword [rdi+0x120 {GfFile::gfDataHead.begin}]
00006646 // Load 0x6
00006646 8b7734 mov esi, dword [rdi+0x34 {GfFile::headerBuffer.__offset(0x24).d}]
00006649 4889d0 mov rax, rdx
0000664c // Multiply by 0x80000001
0000664c //
0000664c // This is an overflow
0000664c 0faf7730 imul esi, dword [rdi+0x30 {GfFile::headerBuffer.__offset(0x20).d}] [1]
00006650 48bf398ee3388ee3…mov rdi, 0x8e38e38e38e38e39
0000665a 4829c8 sub rax, rcx
0000665d 48c1f802 sar rax, 0x2
00006661 480fafc7 imul rax, rdi
00006665 4863f6 movsxd rsi, esi
00006668 4839c6 cmp rsi, rax
0000666b 7753 ja 0x66c0
0000666d 7314 jae 0x6683
0000666f 488d04f6 lea rax, [rsi+rsi*8]
00006673 488d0481 lea rax, [rcx+rax*4]
00006677 4839c2 cmp rdx, rax
0000667a 7407 je 0x6683
0000667c 48898328010000 mov qword [rbx+0x128 {GfFile::gfDataHead.end}], rax
00006683 48637338 movsxd rsi, dword [rbx+0x38 {GfFile::headerBuffer.datHeadVecOffset}]
00006687 488b7b08 mov rdi, qword [rbx+0x8 {GfFile::GfFilePointer}]
0000668b 31d2 xor edx, edx {0x0}
0000668d e87ebcffff call fseek
00006692 // Load 0xffffffff80000001
00006692 48635330 movsxd rdx, dword [rbx+0x30 {GfFile::headerBuffer.__offset(0x20).d}]
00006696 // Load 0x6
00006696 48634334 movsxd rax, dword [rbx+0x34 {GfFile::headerBuffer.__offset(0x24).d}]
0000669a be01000000 mov esi, 0x1
0000669f 488b4b08 mov rcx, qword [rbx+0x8 {GfFile::GfFilePointer}]
000066a3 488bbb20010000 mov rdi, qword [rbx+0x120 {GfFile::gfDataHead.begin}]
000066aa // Same multiply as earlier, but with 64-bit registers
000066aa 480fafc2 imul rax, rdx [3]
000066ae 488d14c0 lea rdx, [rax+rax*8]
000066b2 48c1e202 shl rdx, 0x2
000066b6 // This fread will read in the un-overflowed value of bytes into a buffer only sized for
000066b6 // the overflowed 32 bit value
000066b6 e8d5bcffff call fread [4]
000066bb 31c0 xor eax, eax {0x0}
000066bd 5b pop rbx {__saved_rbx}
000066be c3 retn {__return_addr}
000066c0 4829c6 sub rsi, rax
000066c3 488dbb20010000 lea rdi, [rbx+0x120]
000066ca e821020000 call std::vector<GfDatHead_t,...tor<GfDatHead_t> >::_M_default_append [2]
000066cf ebb2 jmp 0x6683
Crash Information
---CRASH SUMMARY---
Filename: 0/crashes.2021-07-08-06:48:19/id:000003,sig:06,src:000002,time:7983168,op:flip1,pos:35.gf
SHA1: d1e3930a21198a5f47b4a74172e3b521d24b5404
Classification: EXPLOITABLE
Hash: d534e5b0051653dc75a9212440169e08.740bedddcd989b50806d5aa54a764319
Command: ../AnyCubicPluginLinux 0/crashes.2021-07-08-06:48:19/id:000003,sig:06,src:000002,time:7983168,op:flip1,pos:35.gf out.pwx
Faulting Frame:
operator new(unsigned long) @ 0x00007ffff7e78b39: in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.28
Disassembly:
0x00007ffff7abb8ba: xor edx,edx
0x00007ffff7abb8bc: mov rsi,r9
0x00007ffff7abb8bf: mov edi,0x2
0x00007ffff7abb8c4: mov eax,0xe
0x00007ffff7abb8c9: syscall
=> 0x00007ffff7abb8cb: mov rax,QWORD PTR [rsp+0x108]
0x00007ffff7abb8d3: sub rax,QWORD PTR fs:0x28
0x00007ffff7abb8dc: jne 0x7ffff7abb904 <__GI_raise+260>
0x00007ffff7abb8de: mov eax,r8d
0x00007ffff7abb8e1: add rsp,0x118
Stack Head (12 entries):
__GI_raise @ 0x00007ffff7abb8cb: in (BL)
__GI_abort @ 0x00007ffff7aa0864: in (BL)
__libc_message @ 0x00007ffff7b03af6: in (BL)
malloc_printerr @ 0x00007ffff7b0c46c: in (BL)
_int_malloc @ 0x00007ffff7b0fb14: in (BL)
__GI___libc_malloc @ 0x00007ffff7b115d4: in (BL)
operator @ 0x00007ffff7e78b39: in /usr/lib/x86_64-linux-gnu/libstdc++.so.6.0.28
std::vector<PhotonsLayerH @ 0x0000555555558a01: in /home/fuzz/Desktop/chitubox/resource/plugin/AnycubicPlugin/AnyCubicPluginLinux
PwsFile::WritePrepare(GfF @ 0x00005555555579df: in /home/fuzz/Desktop/chitubox/resource/plugin/AnycubicPlugin/AnyCubicPluginLinux
PwsFile::ZipImages(GfFile @ 0x00005555555588d6: in /home/fuzz/Desktop/chitubox/resource/plugin/AnycubicPlugin/AnyCubicPluginLinux
Encode2GfFile(char @ 0x00005555555569a0: in /home/fuzz/Desktop/chitubox/resource/plugin/AnycubicPlugin/AnyCubicPluginLinux
main @ 0x0000555555556619: in /home/fuzz/Desktop/chitubox/resource/plugin/AnycubicPlugin/AnyCubicPluginLinux
Registers:
rax=0x0000000000000000 rbx=0x00007ffff7a78f80 rcx=0x00007ffff7abb8cb rdx=0x0000000000000000
rsi=0x00007fffffffd560 rdi=0x0000000000000002 rbp=0x00007fffffffd8b0 rsp=0x00007fffffffd560
r8=0x0000000000000000 r9=0x00007fffffffd560 r10=0x0000000000000008 r11=0x0000000000000246
r12=0x00007fffffffd7d0 r13=0x0000000000000010 r14=0x00007ffff7fc7000 r15=0x0000000000000001
rip=0x00007ffff7abb8cb efl=0x0000000000000246 cs=0x0000000000000033 ss=0x000000000000002b
ds=0x0000000000000000 es=0x0000000000000000 fs=0x0000000000000000 gs=0x0000000000000000
Extra Data:
Description: Heap error
Short description: HeapError (10/22)
Explanation: The target's backtrace indicates that libc has detected a heap error or that the target was executing a heap function when it stopped.
---END SUMMARY---
Timeline
2021-09-28 - Vendor Disclosure
2021-10-29- 30 day follow up
2021-11-18 - 45+ day follow up
2021-12-13 - Final follow up
2022-01-10 - Public Release
Discovered by Carl Hurd of Cisco Talos.