libjpeg null pointer dereference vulnerability (CNVD-2021-73919)

libjpeg is a free library written entirely in C to handle the JPEG image data format. libjpeg 2020021 and earlier versions of blockbitmaprequester.cpp contain the BlockBitmapRequester::ReconstructUnsampled() function is vulnerable to a null pointer dereference. An attacker could exploit this vulnerability to cause a denial of service.