Memory corruption via undersized change_dict allocation

Integer overflow in GTKWave 3.3.115 allows attackers to corrupt process memory when a victim opens a crafted VZT file. The vzt_rd_block_vch_decode function multiplies attacker-controlled num_sections and num_dict_entries without checking for overflow, allocates an undersized change_dict buffer, and then writes past its heap boundary. Exploitation requires user interaction; the overwrite causes a crash or, under favorable heap and threading conditions, arbitrary code execution.