Excises uracil residues from the DNA which can arise as a result of misincorporation of dUMP residues by DNA polymerase or due to deamination of cytosine. Hydrolyzes single-stranded DNA or mismatched double-stranded DNA and polynucleotides, releasing free uracil. Belongs to the uracil-DNA glycosylase (UDG) superfamily. UNG family.