hb-ot-layout-gsubgpos.hh in HarfBuzz through 6.0.0 allows attackers to trigger O(n^2) growth via consecutive marks during the process of looking back for base glyphs when attaching marks.
Multiple unspecified vulnerabilities in HarfBuzz before 1.0.6, as used in Google Chrome before 48.0.2564.82, allow attackers to cause a denial of service or possibly have other impact via crafted data, as demonstrated by a buffer over-read resulting from an inverted length check in hb-ot-font.cc, a different issue than CVE-2015-8947.