The FoFiType1::parse function in fofi/FoFiType1.cc in the PDF parser in xpdf before 3.02pl5, poppler 0.8.7 and possibly other versions up to 0.15.1, kdegraphics, and possibly other products allows context-dependent attackers to cause a denial of service (crash) and possibly execute arbitrary code via a PDF file with a crafted PostScript Type1 font that contains a negative array index, which bypasses input validation and triggers memory corruption.
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.