A search is presented for hidden-sector bosons, χ, produced in the decay B0→K∗(892)0χ, with K∗(892)0→K+π− and χ→μ+μ−. The search is performed using pp-collision data corresponding to 3.0  fb−1 collected with the LHCb detector. No significant signal is observed in the accessible mass range 214≤m(χ)≤4350  MeV, and upper limits are placed on the branching fraction product B(B0→K∗(892)0χ)×B(χ→μ+μ−) as a function of the mass and lifetime of the χ boson. These limits are of the order of 10−9 for χ lifetimes less than 100 ps over most of the m(χ) range, and place the most stringent constraints to date on many theories that predict the existence of additional low-mass bosons.