The host is installed with Mozilla Firefox before 38.0, Firefox ESR 31.x before 31.7 or Thunderbird before 31.7 and is prone to an use-after-free vulnerability. A flaw is present in the applications, which fail to handle a document containing crafted text in conjunction with a Cascading Style Sheets (CSS) token sequence containing properties related to vertical text. Successful exploitation could allow attackers to execute arbitrary code or cause a denial of service (heap memory corruption).