Global buffer out-of-bounds read in DCMTK JPEG Huffman decoding

A global out-of-bounds read in the Huffman decoder of the bundled IJG JPEG libraries (dcmjpeg/libijg8, libijg12 and libijg16) of OFFIS DCMTK 3.7.0 allows an attacker to read memory beyond the extend_test[] and extend_offset[] tables, causing incorrectly decoded pixel data or a crash, via a DICOM file with a crafted JPEG stream whose Huffman table defines a difference category above 15. Huffman symbol values are not range-checked unless DCMTK is built with DCMTK_ENABLE_STRICT_HUFFMAN_TABLE_CHECK, which is disabled by default. dcmdjpeg and any application that decompresses JPEG DICOM images with DCMTK are affected. The issue is fixed in commit d6ae1bc8d5b9ae9c7300013c8c85cc2ea0fd8cf5.