The mozilla::dom::OscillatorNodeEngine::ComputeCustom function in the Web Audio subsystem in Mozilla Firefox before 33.0, Firefox ESR 31.x before 31.2, and Thunderbird 31.x before 31.2 allows remote attackers to obtain sensitive information from process memory or cause a denial of service (out-of-bounds read, memory corruption, and application crash) via an invalid custom waveform that triggers a calculation of a negative frequency value.