libjpeg null pointer dereference vulnerability (CNVD-2021-73921)

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 a null pointer dereference vulnerability in the BlockBitmapRequester::PullQData() function. An attacker can exploit this vulnerability to cause a denial of service.