In libopenmpt before 0.3.19 and 0.4.x before 0.4.9, ModPlug_InstrumentName and ModPlug_SampleName in libopenmpt_modplug.c do not restrict the lengths of libmodplug output-buffer strings in the C API, leading to a buffer overflow.
libopenmpt before 0.4.3 allows a crash due to a NULL pointer dereference when doing a portamento from an OPL instrument to an empty instrument note map slot.