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Status: closed-fixed

Owner: nobody

Labels: None

Priority: 5

Updated: 2019-07-29

Created: 2019-02-27

Private: No

Hi,
I found that a crafted png file can lead to an interger overflow bug, which lead to a heap-based buffer overflow bug futher. The vulnerable function is png_compress() of AdvanceCOMP:advpng:pngex.cc:55, version 2.1.

I attach my poc below. You can test it via
/path/to/advpng -z /path/to/poc

The backtrace and ASAN information are as follows:

backtrace

pwndbg> bt full #0 __memcpy_avx_unaligned () at …/sysdeps/x86_64/multiarch/memcpy-avx-unaligned.S:245 No locals. #1 0x0000000000405a31 in png_compress (level=…, out_ptr=…, out_size=@0x7fffffffd93c: 32767, img_ptr=0x662361 ‘\001’ <repeats 32 times>, img_scanline=1, img_pixel=1, x=0, y=0, dx=4294967295, dy=1056) at pngex.cc:55 p1 = 0x662361 ‘\001’ <repeats 32 times> fil_ptr = { data = 0x660de0 "", own = true } fil_size = 0 fil_scanline = 0 z_ptr = { data = 0x660e00 "\230k1\367\377\177", own = true } z_size = 22 i = 0 p0 = 0x660de1 “k1\367\377\177” __PRETTY_FUNCTION__ = "void png_compress(shrink_t, data_ptr&, unsigned int&, const unsigned char*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int)" #2 0x000000000040706f in png_write (f=0x660d10, pix_width=4294967295, pix_height=1056, pix_pixel=1, pix_ptr=0x662361 ‘\001’ <repeats 32 times>, pix_scanline=1, pal_ptr=0x660e30 ‘0’ <repeats 15 times>, pal_size=15, rns_ptr=0x0, rns_size=0, level=…) at pngex.cc:355 ihdr = “\377\377\377\377\000\000\004 \b\003\000\000” z_ptr = { data = 0x0, own = false } z_size = 32767 __PRETTY_FUNCTION__ = “void png_write(adv_fz*, unsigned int, unsigned int, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int, shrink_t)" #3 0x0000000000403420 in write_image (f=0x660d10, pix_width=4294967295, pix_height=1056, pix_pixel=1, pix_ptr=0x662361 ‘\001’ <repeats 32 times>, pix_scanline=1, pal_ptr=0x660e30 ‘0’ <repeats 15 times>, pal_size=15, rns_ptr=0x0, rns_size=0) at repng.cc:101 No locals. #4 0x000000000040366e in convert_f (f_in=0x660c40, f_out=0x660d10) at repng.cc:160 dat_ptr = 0x662360 “” dat_size = 1056 pix_pixel = 1 pix_width = 4294967295 pix_height = 1056 pal_ptr = 0x660e30 ‘0’ <repeats 15 times> pal_size = 15 rns_ptr = 0x0 rns_size = 0 pix_ptr = 0x662361 ‘\001’ <repeats 32 times> pix_scanline = 1 #5 0x00000000004038be in convert_inplace (path="./heap-overflow.png”) at repng.cc:193 f_in = 0x660c40 f_out = 0x660d10 path_dst = “./heap-overflow.png.tmp1551203033” __PRETTY_FUNCTION__ = "void convert_inplace(const string&)" dst_size = 0 #6 0x00000000004040a4 in rezip_single (file="./heap-overflow.png", total_0=@0x7fffffffe300: 0, total_1=@0x7fffffffe308: 0) at repng.cc:283 size_0 = 218 size_1 = 0 desc = “” __PRETTY_FUNCTION__ = "void rezip_single(const string&, long long unsigned int&, long long unsigned int&)" #7 0x000000000040443f in rezip_all (argc=1, argv=0x7fffffffe578) at repng.cc:317 i = 0 total_0 = 0 total_1 = 0 #8 0x0000000000404c8a in process (argc=3, argv=0x7fffffffe568) at repng.cc:476 cmd = cmd_recompress c = -1 __PRETTY_FUNCTION__ = "void process(int, char**)" #9 0x0000000000404e54 in main (argc=3, argv=0x7fffffffe568) at repng.cc:489 No locals. #10 0x00007ffff6f72830 in __libc_start_main (main=0x404e24 <main(int, char**)>, argc=3, argv=0x7fffffffe568, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffe558) at …/csu/libc-start.c:291 result = <optimized out> unwind_buf = { cancel_jmp_buf = {{ jmp_buf = {0, 2691200841703839888, 4206080, 140737488348512, 0, 0, -2691200322350786416, -2691184995872188272}, mask_was_saved = 0 }}, priv = { pad = {0x0, 0x0, 0x7fffffffe588, 0x7ffff7ffe168}, data = { prev = 0x0, cleanup = 0x0, canceltype = -6776 } } } not_first_call = <optimized out> #11 0x0000000000402e29 in _start () No symbol table info available. pwndbg>

ASAN

ubuntu@VM-61-71-ubuntu:~$ ./advpng-asan -z ./heap-overflow.png

==11954==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x6190000068a0 at pc 0x7f5e2e4f0935 bp 0x7ffe805dec50 sp 0x7ffe805de3f8 READ of size 4294967295 at 0x6190000068a0 thread T0 #0 0x7f5e2e4f0934 in __asan_memcpy (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x8c934) #1 0x411173 in memcpy /usr/include/x86_64-linux-gnu/bits/string3.h:53 #2 0x411173 in png_compress(shrink_t, data_ptr&, unsigned int&, unsigned char const*, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int, unsigned int) /home/ubuntu/advancecomp-2.1/pngex.cc:55 #3 0x41756f in png_write(adv_fz_struct*, unsigned int, unsigned int, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int, shrink_t) /home/ubuntu/advancecomp-2.1/pngex.cc:355 #4 0x406d46 in write_image(adv_fz_struct*, unsigned int, unsigned int, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int, unsigned char*, unsigned int) /home/ubuntu/advancecomp-2.1/repng.cc:101 #5 0x406f2a in convert_f(adv_fz_struct*, adv_fz_struct*) /home/ubuntu/advancecomp-2.1/repng.cc:160 #6 0x4071e6 in convert_inplace(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&) /home/ubuntu/advancecomp-2.1/repng.cc:193 #7 0x4088c6 in rezip_single(std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> > const&, unsigned long long&, unsigned long long&) /home/ubuntu/advancecomp-2.1/repng.cc:283 #8 0x4096c1 in rezip_all(int, char**) /home/ubuntu/advancecomp-2.1/repng.cc:317 #9 0x40d5c6 in process(int, char**) /home/ubuntu/advancecomp-2.1/repng.cc:476 #10 0x4034a4 in main /home/ubuntu/advancecomp-2.1/repng.cc:489 #11 0x7f5e2d5ff82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f) #12 0x404a28 in _start (/home/ubuntu/advpng-asan+0x404a28)

0x6190000068a0 is located 0 bytes to the right of 1056-byte region [0x619000006480,0x6190000068a0) allocated by thread T0 here: #0 0x7f5e2e4fc602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602) #1 0x43e94f in adv_png_read_ihdr lib/png.c:723

SUMMARY: AddressSanitizer: heap-buffer-overflow ??:0 __asan_memcpy Shadow bytes around the buggy address: 0x0c327fff8cc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c327fff8cd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c327fff8ce0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c327fff8cf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 0x0c327fff8d00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 =>0x0c327fff8d10: 00 00 00 00[fa]fa fa fa fa fa fa fa fa fa fa fa 0x0c327fff8d20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c327fff8d30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c327fff8d40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c327fff8d50: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 0x0c327fff8d60: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa 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 Heap right redzone: fb Freed heap region: fd Stack left redzone: f1 Stack mid redzone: f2 Stack right redzone: f3 Stack partial redzone: f4 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 ==11954==ABORTING

After debugging, I found improper size of the png is the reason.

For example, if I modify the size of a png to -1 x 1056, 4-bit colormap, with advpng running, the function png_compress() gets a set of arguments as
#1 0x0000000000405a31 in png_compress (level=..., out_ptr=..., out_size=@0x7fffffffd93c: 32767, img_ptr=0x662361 '\001' <repeats 32 times>, img_scanline=1, img_pixel=1, x=0, y=0, dx=4294967295, dy=1056) at pngex.cc:55,
where dx equals the width of the png, dy equals the hight of the png and img_pixel depends on the bit depth.
As a result, the following code goes as:

# pngex.cc 33 void png_compress(shrink_t level, data_ptr& out_ptr, unsigned& out_size, const unsigned char* img_ptr, unsigned img_scanline, unsigned img_pixel, unsigned x, unsigned y, unsigned dx, unsigned dy) 34 { 35 data_ptr fil_ptr; 36 unsigned fil_size; 37 unsigned fil_scanline; 38 data_ptr z_ptr; 39 unsigned z_size; 40 unsigned i; 41 unsigned char* p0; 42 43 fil_scanline = dx * img_pixel + 1; # fil_scanline = 0xffffffff * 1 + 1 = 0, interger overflow happens 44 fil_size = dy * fil_scanline; # fil_size = 1056 * 0 = 0 45 z_size = oversize_zlib(fil_size);
46 47 fil_ptr = data_alloc(fil_size); # malloc(0), align to 0x10 48 z_ptr = data_alloc(z_size); 49 50 p0 = fil_ptr; 51 52 for(i=0;i<dy;++i) { 53 const unsigned char* p1 = &img_ptr[x * img_pixel + (i+y) * img_scanline]; 54 *p0++ = 0; 55 memcpy(p0, p1, dx * img_pixel); # dx * img_pixel = 0xffffffff, while size of p0 is 0x10, buffer overflow happens.

e-mail: [email protected]****Discoverer: M4x@Chaitin Security Research Lab

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