Embedded defects are classical solutions of the field equations of motion which are unstable in the absence of a fluctuating background. Such embedded defect configurations exist in the standard model of particle physics, both in the electroweak theory and in a low-energy model for QCD. As will be discussed, a wide class of embedded defects, in particular those in the electroweak theory, can be stabilized by plasma effects which are inevitably present in the early Universe. Therefore, embedded defects may play an important role in early Universe cosmology. As a particular application, it will be pointed out that stabilized pion strings will generated primordial magnetic fields with astrophysically relevant coherence lengths.