In Xpdf 4.01.01, a heap-based buffer over-read could be triggered in SampledFunction::transform in Function.cc when using a large index for samples. It can, for example, be triggered by sending a crafted PDF document to the pdftotext tool. It allows an attacker to use a crafted pdf file to cause Denial of Service or an information leak, or possibly have unspecified other impact.
The product reads data past the end, or before the beginning, of the intended buffer.