Created attachment 132065 [details]
Proof of concept

There is a bug reading outside bounds at Functions.cc:218

 212 }
 213 
 214 void IdentityFunction::transform(double *in, double *out) {
 215   int i;
 216 
 217   for (i = 0; i < funcMaxOutputs; ++i) {
 218     out[i] = in[i];
 219   }
 220 }

funcMacOutputs is defined in Functions.h:
#define funcMaxOutputs       32

Parsing the PoC.pdf, this function is called from GfxFunctionShading::getColor:

3957 void GfxFunctionShading::getColor(double x, double y, GfxColor *color) {
3958   double in[2], out[gfxColorMaxComps];
3959   int i;
3960 
3961   // NB: there can be one function with n outputs or n functions with
3962   // one output each (where n = number of color components)
3963   for (i = 0; i < gfxColorMaxComps; ++i) {
3964     out[i] = 0;
3965   }
3966   in[0] = x;
3967   in[1] = y;
3968   for (i = 0; i < nFuncs; ++i) {
3969     funcs[i]->transform(in, &out[i]);
3970   }
3971   for (i = 0; i < gfxColorMaxComps; ++i) {
3972     color->c[i] = dblToCol(out[i]);
3973   }
3974 }

Where the variable in has only 2 elements, instead of the 32 read at IdentityFunction::transform. So 30 elements are read after the in.

This could be fixed increasing the number of elements for the variable in:
3958   double in[gfxColorMaxComps], out[gfxColorMaxComps];

PoC is attached.

This vulnerability has been found by Offensive Research at Salesforce.com:
Alberto Garcia (@algillera), Francisco Oca (@francisco_oca) & Suleman Ali (@Salbei_)