The police also acknowledged the concerns in the report and said it would "continue to discuss these with the event organisers before providing a response".
The festival and the police must respond to the report by 26 September.
Mr Walker, area coroner for Hampshire, Portsmouth and Southampton, said he had taken into account the changes made by the festival and the police for Boomtown 2025 before making his comments.
"I heard evidence that illegal drugs were freely available to purchase at the festival," he said.
"One of Ben's friends described how dealers would walk through the campsites shouting the names of the drugs they were offering to supply.
"I was told this took place as regularly as every 20 minutes and that they saw nothing done to try and disrupt this trade.
"I am concerned that an unchecked, open and free trade in unlawful drugs will create a risk of future deaths."
Mr Walker said he had heard evidence that people carrying drugs on the site were only ejected if they were quantities "consistent with being a drug dealer".
He said he was concerned about that police adding that there is "no disincentive" for festival-goers who attempt to bring drugs into the event and could "give rise to risk of future death".