The get_group_tree function in lib/Munin/Master/HTMLConfig.pm in Munin before 2.0.18 allows remote nodes to cause a denial of service (infinite loop and memory consumption in the munin-html process) via crafted multigraph data.
https://github.com/munin-monitoring/munin/commit/284d7402718d98fcf10cee565415939882abab99
https://github.com/munin-monitoring/munin/blob/2.0.18/ChangeLog