Integer overflow in the PL_ARENA_ALLOCATE implementation in Netscape Portable Runtime (NSPR) in Mozilla Network Security Services (NSS) before 3.19.2.1 and 3.20.x before 3.20.1, as used in Firefox before 42.0 and Firefox ESR 38.x before 38.4 and other products, allows remote attackers to execute arbitrary code or cause a denial of service (memory corruption and application crash) via unspecified vectors.