CVE-2019-19787: ATasm: 6502 cross-assembler / Bugs

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#10 Stack-based buffer overflow in the get_signed_expression() function

Status: closed

Owner: nobody

Labels: None

Priority: 5

Updated: 2021-03-20

Created: 2019-12-13

Private: No

Hi,

While fuzzing ATasm 1.08 with Honggfuzz, I found a stack-based buffer overflow in the get_signed_expression() function, in setparse.c.

Attaching a reproducer, issue can be reproduced by running:

================================================================= ==10633==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffe5c1b3480 at pc 0x0000004e27ea bp 0x7ffe5c1b3210 sp 0x7ffe5c1b3208 WRITE of size 1 at 0x7ffe5c1b3480 thread T0 #0 0x4e27e9 in get_signed_expression /home/fcambus/atasm/src/setparse.c:179:14 #1 0x4e08a5 in get_expression /home/fcambus/atasm/src/setparse.c:154:27 #2 0x4c8de1 in add_label /home/fcambus/atasm/src/asm.c #3 0x4d5563 in do_cmd /home/fcambus/atasm/src/asm.c:1934:5 #4 0x4d5b46 in assemble /home/fcambus/atasm/src/asm.c:1980:9 #5 0x4d8082 in main /home/fcambus/atasm/src/asm.c:2392:3 #6 0x7f1cbb2811e2 in __libc_start_main /build/glibc-4WA41p/glibc-2.30/csu/…/csu/libc-start.c:308:16 #7 0x41b3fd in _start (/home/fcambus/atasm/atasm+0x41b3fd)

Address 0x7ffe5c1b3480 is located in stack of thread T0 at offset 608 in frame #0 0x4e08bf in get_signed_expression /home/fcambus/atasm/src/setparse.c:157

This frame has 4 object(s): [32, 288) ‘err.i’ (line 136) [352, 608) ‘buf’ (line 158) <== Memory access at offset 608 overflows this variable [672, 928) ‘work’ (line 158) [992, 1005) ‘math’ (line 162) HINT: this may be a false positive if your program uses some custom stack unwind mechanism, swapcontext or vfork (longjmp and C++ exceptions *are* supported) SUMMARY: AddressSanitizer: stack-buffer-overflow /home/fcambus/atasm/src/setparse.c:179:14 in get_signed_expression Shadow bytes around the buggy address: 0x10004b82e640: 00 00 00 00 f1 f1 f1 f1 f8 f8 f8 f8 f8 f8 f8 f8 0x10004b82e650: f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 f8 0x10004b82e660: f8 f8 f8 f8 f8 f8 f8 f8 f2 f2 f2 f2 f2 f2 f2 f2 0x10004b82e670: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10004b82e680: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x10004b82e690:[f2]f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 0x10004b82e6a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10004b82e6b0: 00 00 00 00 00 00 00 00 f2 f2 f2 f2 f2 f2 f2 f2 0x10004b82e6c0: 00 05 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00 0x10004b82e6d0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10004b82e6e0: 00 00 00 00 f1 f1 f1 f1 f8 f8 f8 f8 f8 f8 f8 f8 Shadow byte legend (one shadow byte represents 8 application bytes): Addressable: 00 Partially addressable: 01 02 03 04 05 06 07 Heap left redzone: fa Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack after return: f5 Stack use after scope: f8 Global redzone: f9 Global init order: f6 Poisoned by user: f7 Container overflow: fc Array cookie: ac Intra object redzone: bb ASan internal: fe Left alloca redzone: ca Right alloca redzone: cb Shadow gap: cc ==10633==ABORTING

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