Descrizione di CVE-2022-41220

md2roff 1.9 soffre di un buffer overflow basato sullo stack tramite un file Markdown contenente un gran numero di caratteri consecutivi da elaborare.

Riproduzione

Per riprodurre la vulnerabilità, scarica una versione vulnerabile di md2roff (versione 1.9):

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

Una volta compilato il progetto, possiamo elaborare un file markdown malevolo prodotto dai nostri test di fuzzing per riprodurre un crash del programma:

./md2roff poc.md

Eseguendo il comando precedente si produrrà un segfault:

segmentation fault  ./md2roff poc.md

Compilando il progetto con address sanitizer (ASAN) si conferma il nostro stack buffer overflow:

#
#       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 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

Collegamento di GDB

Se esegui il programma con gdb, puoi vedere che i registri vengono sovrascritti dal nostro grande buffer di caratteri: