yasm expand_mmacro function denial of service vulnerability

yasm is a completely rewritten Netwide assembler from yasm open source. yasm version 1.3.0 suffers from a denial of service vulnerability that stems from the presence of a NULL pointer dereference in the expand_mmacro() function in modules/preprocs/nasm/nasm-pp.c. An attacker could exploit the vulnerability to cause a denial of service.