Description de la CVE-2022-41220

md2roff 1.9 souffre d'un débordement de tampon basé sur la pile via un fichier Markdown contenant un grand nombre de caractères consécutifs à traiter.

Reproduction

Pour reproduire la vulnérabilité, téléchargez une version vulnérable de md2roff (version 1.9) :

git clone https://github.com/nereusx/md2roff.git
cd md2roff
git checkout 9241b8cfeb687c57099f3ef45f03a8ad3f291cf4
make

Une fois le projet compilé, nous pouvons traiter un fichier markdown malveillant produit par nos tests de fuzzing pour reproduire un crash du programme :

./md2roff poc.md

L'exécution de la commande précédente produira un segfault :

segmentation fault  ./md2roff poc.md

Compiler le projet avec address sanitizer (ASAN) confirme notre débordement de tampon de pile :

#
#       GNU make
#

prefix  ?= /usr/local
bindir  ?= $(prefix)/bin
mandir  ?= $(prefix)/share/man
man1dir ?= $(mandir)/man1

LIBS   = -lc
CFLAGS = -std=c99 -fsanitize=address

all: md2roff md2roff.1.gz

md2roff: md2roff.c
        $(CC) $(CFLAGS) md2roff.c -o md2roff $(LDFLAGS) $(LIBS)

md2roff.1.gz: md2roff.md md2roff
        ./md2roff --synopsis-style=1 md2roff.md > md2roff.1
        -groff md2roff.1 -Tpdf -man -P -e > md2roff.1.pdf
        ./md2roff -z --synopsis-style=1 md2roff.md > md2roff.1
        gzip -f md2roff.1

install: md2roff md2roff.1.gz
        mkdir -p -m 0755 $(DESTDIR)$(bindir) $(DESTDIR)$(man1dir)
        install -m 0755 -s md2roff $(DESTDIR)$(bindir)
        install -m 0644 md2roff.1.gz $(DESTDIR)$(man1dir)

uninstall:
        rm -f $(DESTDIR)$(bindir)/md2roff $(DESTDIR)$(man1dir)/md2roff.1.gz

clean:
        rm -f *.o md2roff md2roff.1*

$ ./md2roff poc.md ================================================================= ==15685==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7ffedb68e230 at pc 0x55ab4ac56d64 bp 0x7ffedb68e020 sp 0x7ffedb68e018 WRITE of size 1 at 0x7ffedb68e230 thread T0 #0 0x55ab4ac56d63 in md2roff (/home/kali/projects/fuzzing/fuzz_targets/md2roff/md2roff+0x10d63) #1 0x55ab4ac598c0 in main (/home/kali/projects/fuzzing/fuzz_targets/md2roff/md2roff+0x138c0) #2 0x7f589f446189 in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58 #3 0x7f589f446244 in __libc_start_main_impl ../csu/libc-start.c:381 #4 0x55ab4ac4d3a0 in _start (/home/kali/projects/fuzzing/fuzz_targets/md2roff/md2roff+0x73a0) Address 0x7ffedb68e230 is located in stack of thread T0 at offset 80 in frame #0 0x55ab4ac50d7e in md2roff (/home/kali/projects/fuzzing/fuzz_targets/md2roff/md2roff+0xad7e) This frame has 6 object(s): [32, 40) 'tt' (line 724) [64, 80) 'num' (line 1140) <== Memory access at offset 80 overflows this variable [96, 352) 'secname' (line 662) [416, 672) 'appname' (line 662) [736, 992) 'appsec' (line 662) [1056, 1312) 'appdate' (line 662) 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/kali/projects/fuzzing/fuzz_targets/md2roff/md2roff+0x10d63) in md2roff Shadow bytes around the buggy address: 0x10005b6c9bf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c30: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 =>0x10005b6c9c40: f8 f2 f2 f2 00 00[f2]f2 00 00 00 00 00 00 00 00 0x10005b6c9c50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c60: 00 00 00 00 00 00 00 00 f2 f2 f2 f2 f2 f2 f2 f2 0x10005b6c9c70: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x10005b6c9c90: f2 f2 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00 00 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 ==15685==ABORTING

pwndbg> r poc.md Starting program: /dev/shm/CVE-2022-41220/md2roff/md2roff poc.md [Thread debugging using libthread_db enabled] Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1". .\# roff document .\# DO NOT MODIFY THIS FILE! It was generated by md2roff .do mso man.tmac .TH poc.md 7 2023-07-27 document Gl|||||n Program received signal SIGSEGV, Segmentation fault. 0x0000555555556d0a in println () LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA ─────────────────────────────────────────────────────────────[ REGISTERS / show-flags off / show-compact-regs off ]───────────────────────────────────────────────────────────── *RAX 0x3277413177413077 ('w0Aw1Aw2') RBX 0x7fffffffddb8 ◂— 0x3072423971423871 ('q8Bq9Br0') *RCX 0x0 *RDX 0x0 *RDI 0x3277413177413077 ('w0Aw1Aw2') *RSI 0x2048532e R8 0x7 R9 0x555555561200 ◂— 0x555555561 *R10 0x7ffff7de10f8 ◂— 0x10001a00001033 *R11 0x7ffff7f1ffe0 (__strchr_avx2) ◂— vmovd xmm0, esi R12 0x0 R13 0x7fffffffddd0 ◂— 0x3872423772423672 ('r6Br7Br8') R14 0x55555555edd8 (__do_global_dtors_aux_fini_array_entry) —▸ 0x555555556300 (__do_global_dtors_aux) ◂— endbr64 R15 0x7ffff7ffd020 (_rtld_global) —▸ 0x7ffff7ffe2e0 —▸ 0x555555554000 ◂— 0x10102464c457f *RBP 0x7fffffffd550 —▸ 0x7fffffffdb60 ◂— 0x3078413977413877 ('w8Aw9Ax0') *RSP 0x7fffffffd530 —▸ 0x555555561cc0 ◂— 0x7c7c7c7c806c4708 *RIP 0x555555556d0a (println+73) ◂— movzx eax, byte ptr [rax] ──────────────────────────────────────────────────────────────────────[ DISASM / x86-64 / set emulate on ]────────────────────────────────────────────────────────────────────── ► 0x555555556d0a <println+73> movzx eax, byte ptr [rax]

CVE-2022-41220

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