podofo: NULL pointer dereference in GraphicsStack::TGraphicsStackElement::SetNonStrokingColorSpace (graphicsstack.h)

Description:
podofo is a C++ library to work with the PDF file format.

A fuzz on it discovered a null pointer dereference. The upstream project denies me to open a new ticket. So, I just will forward this on the -users mailing list.

The complete ASan output:

# podofocolor dummy $FILE foo
==32192==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x000000525f24 bp 0x7ffe0a1fdc90 sp 0x7ffe0a1fdc00 T0)
==32192==The signal is caused by a READ memory access.
==32192==Hint: address points to the zero page.
    #0 0x525f23 in GraphicsStack::TGraphicsStackElement::SetNonStrokingColorSpace(PoDoFo::EPdfColorSpace) /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/graphicsstack.h:83:38
    #1 0x525f23 in GraphicsStack::SetNonStrokingColorSpace(PoDoFo::EPdfColorSpace) /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/graphicsstack.h:129
    #2 0x525f23 in ColorChanger::ProcessColor(ColorChanger::EKeywordType, int, std::vector<PoDoFo::PdfVariant, std::allocator >&, GraphicsStack&) /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/colorchanger.cpp:478
    #3 0x521b3c in ColorChanger::ReplaceColorsInPage(PoDoFo::PdfCanvas*) /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/colorchanger.cpp:214:31
    #4 0x51ed8e in ColorChanger::start() /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/colorchanger.cpp:120:15
    #5 0x51c06d in main /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/podofocolor.cpp:116:12
    #6 0x7fc21680761f in __libc_start_main /var/tmp/portage/sys-libs/glibc-2.22-r4/work/glibc-2.22/csu/libc-start.c:289
    #7 0x428718 in _start (/usr/bin/podofocolor+0x428718)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /tmp/portage/app-text/podofo-0.9.4/work/podofo-0.9.4/tools/podofocolor/graphicsstack.h:83:38 in GraphicsStack::TGraphicsStackElement::SetNonStrokingColorSpace(PoDoFo::EPdfColorSpace)
==32192==ABORTING

Affected version:
0.9.4

Fixed version:
N/A

Commit fix:
N/A

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
CVE-2017-6846

Reproducer:
https://github.com/asarubbo/poc/blob/master/00173-podofo-nullptr-GraphicsStack-TGraphicsStackElement-SetNonStrokingColorSpace

Timeline:
2017-02-13: bug discovered
2017-03-02: bug reported to upstream
2017-03-02: blog post about the issue
2017-03-12: CVE assigned

Note:
This bug was found with American Fuzzy Lop.

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podofo: NULL pointer dereference in GraphicsStack::TGraphicsStackElement::SetNonStrokingColorSpace (graphicsstack.h)