Probably a misprint for vvurt; that is, wurt. If so, then it is the past subjunctive from Proto-Germanic *werþaną. Compare Gothic 𐍅𐌰𐌿𐍂𐌸𐌹 (waurþi) (from 𐍅𐌰𐌹𐍂𐌸𐌰𐌽 (wairþan)).
vburt