It is not yet clear what the sale means for the future of the event or staff at UBM, including the event's director, James Samuel, who was promoted to the role in September 2012. Samuel also became president of MPI UK in July this year.
Confex is one of the UK's leading exhibitions for the events industry and celebrated its 30th anniversary in March.
Following this year's event, industry figures continued to question the value of the show after it failed to boost visitor numbers.
The acquisition will be Mash Media's second in two years, following the purchase of The Event Production Show from Ocean Media Group, alongside the Event Production Awards, in June 2012.
Despite attempts by C&IT to contact Mash Media's managing director Julian Agostini, he was unavailable to comment.
UBM has also declined to comment. It was announced this week that UBM CEO David Levin is to step down in 2014.
More to follow.