In this talk, closed bosonic strings propagating in a flat background with constant H-flux as well as in its T-dual configurations are studied. For that purpose, a conformal field theory capturing linear effects in the flux will be defined and scattering amplitudes of tachyon vertex operators will be computed. In the resulting expressions, the Rogers dilogarithm plays a prominent role. Furthermore, indications for a nonassociative structure are found, which can be described in terms of a deformed tri-product. Finally, it is argued that the non-geometric R-flux background flows to an asymmetric CFT.