There is an invalid memory access in the function fprintf located in Error.cc in Xpdf 4.0.2. It can be triggered by sending a crafted PDF file to the pdftohtml binary, which allows a remote attacker to cause a Denial of Service (Segmentation fault) or possibly have unspecified other impact.
CWE-787 - Out-of-Bounds Write
Out-of-bounds write vulnerability is a memory access bug that allows software to write data past the end or before the beginning of the intended buffer. This may result in the corruption of data, a crash, or arbitrary code execution.