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[2015-11-26 11:16 UTC] emmanuel dot law at gmail dot com
Description:
------------
This is the function prototype for ImageRotate:
resource imagerotate ( resource $image , float $angle , int $bgd_color [, int $ignore_transparent = 0 ] )
$bgd_color specifies the background color of an image have it has been rotated. This is passed in as an integer that represents an index to the color palette.
There is a lack of validation of $bgd_color. One can pass in a large number that exceeds the color palette array. This reads memory beyond the color palette. Information of the memory leak can then be obtained via the background color after the image has been rotated.
Test script:
---------------
./configure --with-gd
1) Pass in a large $bgd_color:
php -r "imagerotate(imagecreate(1,1),45,0x7ffffff9);"
2) This causes it to crash at gd_interpolation.c:2174 :
Stopped reason: SIGSEGV
0x00000000005fb0b4 in gdImageRotateInterpolated (src=0x7ffff7fb5b38, angle=45, bgcolor=0x7ffffff9) at php-5.6.15/ext/gd/libgd/gd_interpolation.c:2174
2174 bgcolor = gdTrueColorAlpha(src->red[bgcolor], src->green[bgcolor], src->blue[bgcolor], src->alpha[bgcolor]);
gdb-peda$ bt
#0 0x00000000005fb0b4 in gdImageRotateInterpolated (src=0x7ffff7fb5b38, angle=45, bgcolor=0x7ffffff9) at /home/elaw/php-5.6.15/ext/gd/libgd/gd_interpolation.c:2174
#1 0x00000000005d0b73 in zif_imagerotate (ht=0x3, return_value=0x7ffff7fb5810, return_value_ptr=0x7ffff7f80090, this_ptr=0x0, return_value_used=0x0)
at /home/elaw/php-5.6.15/ext/gd/gd.c:2111
#2 0x0000000000850915 in zend_do_fcall_common_helper_SPEC (execute_data=0x7ffff7f800c8) at /home/elaw/php-5.6.15/Zend/zend_vm_execute.h:558
#3 0x000000000085856c in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0x7ffff7f800c8) at /home/elaw/php-5.6.15/Zend/zend_vm_execute.h:2602
#4 0x000000000084ee1a in execute_ex (execute_data=0x7ffff7f800c8) at /home/elaw/php-5.6.15/Zend/zend_vm_execute.h:363
#5 0x000000000084f806 in zend_execute (op_array=0x7ffff7fb42f8) at /home/elaw/php-5.6.15/Zend/zend_vm_execute.h:388
#6 0x00000000007f6636 in zend_eval_stringl (str=0x106ff80 "imagerotate(imagecreate(1,1),45,2147483641);", str_len=0x2c, retval_ptr=0x0,
string_name=0xd46ac4 "Command line code") at /home/elaw/php-5.6.15/Zend/zend_execute_API.c:1077
#7 0x00000000007f68bc in zend_eval_stringl_ex (str=0x106ff80 "imagerotate(imagecreate(1,1),45,2147483641);", str_len=0x2c, retval_ptr=0x0,
string_name=0xd46ac4 "Command line code", handle_exceptions=0x1) at /home/elaw/php-5.6.15/Zend/zend_execute_API.c:1124
#8 0x00000000007f6940 in zend_eval_string_ex (str=0x106ff80 "imagerotate(imagecreate(1,1),45,2147483641);", retval_ptr=0x0, string_name=0xd46ac4 "Command line code",
handle_exceptions=0x1) at /home/elaw/php-5.6.15/Zend/zend_execute_API.c:1135
#9 0x000000000092ce99 in do_cli (argc=0x3, argv=0x106ff00) at /home/elaw/php-5.6.15/sapi/cli/php_cli.c:1034
#10 0x000000000092ddc5 in main (argc=0x3, argv=0x106ff00) at /home/elaw/php-5.6.15/sapi/cli/php_cli.c:1378
#11 0x00007ffff6027b45 in __libc_start_main (main=0x92d722 <main>, argc=0x3, argv=0x7fffffffe338, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>,
stack_end=0x7fffffffe328) at libc-start.c:287
#12 0x0000000000421409 in _start ()
3) One can see that the color platte only has 256 entries:
gdb-peda$ ptype src
type = struct gdImageStruct {
......
int red[256];
int green[256];
int blue[256];
....
4) Thus we are encountering an array index out of bounds.
5) I've created a full exploit that reads large contiguous chunk of memory. The POC can be obtained from https://www.dropbox.com/s/bwuivbug62ki4cs/gdImageRotateInterpolated_Array_Index_OOB_MEM_Read.php?dl=0
./php gdImageRotateInterpolated_Array_Index_OOB_MEM_Read.php
0c40 01 00 00 00 01 00 00 00 01 00 00 00 01 00 00 00 ........ ........
0c50 01 00 00 00 01 00 00 00 01 00 00 00 01 00 00 9d ........ .......�
0c60 01 00 00 9d 01 00 00 fd 01 00 00 00 01 00 00 00 ...�...� ........
0c70 01 00 00 ef 01 00 00 00 01 00 00 2f 01 00 00 00 ...�.... .../....
0c80 01 00 00 20 01 00 00 ff 01 00 00 c8 01 00 00 ff ... ...� ...�...�
0c90 01 00 00 20 01 00 00 ff 01 00 00 c8 01 00 00 ff ... ...� ...�...�
0ca0 01 00 00 70 01 00 00 ff 01 00 00 60 01 00 00 ff ...p...� ...`...�
0cb0 01 00 00 08 01 00 00 ff 01 00 00 b0 01 00 00 ff .......� ...�...�
0cc0 01 00 00 58 01 00 00 ff 01 00 00 88 01 00 00 ff ...X...� ...�...�
0cd0 01 00 00 30 01 00 00 ff 01 00 00 d8 01 00 00 ff ...0...� ...�...�
0ce0 01 00 00 80 01 00 00 ff 01 00 00 28 01 00 00 ff ...�...� ...(...�
0cf0 01 00 00 d0 01 00 00 ff 01 00 00 58 01 00 00 ff ...�...� ...X...�
0d00 01 00 00 00 01 00 00 ff 01 00 00 a8 01 00 00 ff .......� ...�...�
0d10 01 00 00 50 01 00 00 ff 01 00 00 f8 01 00 00 ff ...P...� ...�...�
0d20 01 00 00 a0 01 00 00 ff 01 00 00 d8 01 00 00 ff ...�...� ...�...�
0d30 01 00 00 80 01 00 00 ff 01 00 00 28 01 00 00 ff ...�...� ...(...�
0d40 01 00 00 d0 01 00 00 ff 01 00 00 78 01 00 00 ff ...�...� ...x...�
0d50 01 00 00 20 01 00 00 ff 01 00 00 f0 01 00 00 ff ... ...� ...�...�
0d60 01 00 00 98 01 00 00 ff 01 00 00 40 01 00 00 ff ...�...� ...@...�
.....
6) I've attached a patch for ext/gd/libgd/gd_interpolation.c. For your consideration.
PatchesPull RequestsHistoryAllCommentsChangesGit/SVN commits
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Last updated: Tue Dec 03 17:01:29 2024 UTC |
Hi, Thanks for the patch! It is however incomplete, gdMaxColors apply only to palette image. True colors image can have color values ARGB where the integer representation is bigger that gdMaxColors. It should be: if (bgcolor < 0 || (!im->trueColor && bgcolor >= gdMaxColors)) { I do not have git access right now, it would be nice if you can update the fix accordingly. Thanks!As I took a 2nd thought about it, getting my memory back about what I did in this implementation, a better patch is to move this check after: if (src->trueColor == 0) { if (bgcolor >= 0) { bgcolor = gdTrueColorAlpha(src->red[bgcolor], src->green[bgcolor], src->blue[bgcolor], src->alpha[bgcolor]); } gdImagePaletteToTrueColor(src); } As this function only accepts truecolor, it converts the image to truecolor prior to any operation. The check only needs to be bgcolor < 0 then as true color values can be anything > 0.I don't have permissions to see the commits but the first post by pajoye makes sense. The 2nd however doesn't IMHO. It is still exploitable if we do the check after: if (src->trueColor == 0) { if (bgcolor >= 0) { bgcolor = gdTrueColorAlpha(src->red[bgcolor], src->green[bgcolor], src->blue[bgcolor], src->alpha[bgcolor]); } gdImagePaletteToTrueColor(src); }@emmanuel You are right. Sorry for the confusion, some coffee is needed :) the check should be done in this true clause (for palette images), like: if (bgcolor < 0) { return NULL; } if (src->trueColor == 0) { if (bgcolor <= gdMaxColors) { bgcolor = gdTrueColorAlpha(src->red[bgcolor], src->green[bgcolor], src->blue[bgcolor], src->alpha[bgcolor]); } gdImagePaletteToTrueColor(src); }