Multidict is an implementation of a multidict data structure. From 6.7.0 until 6.9.1, the C extension's items-view reflected union operation, operand | d.items(), in multidictitemsviewor2impl and subtraction operation, d.items() - operand, in multidictitemsviewsub1impl fail to release new key-identity and value references returned for each operand element. Applications that perform these operations over attacker-influenced sequences can leak two strong references per element, and garbage collection cannot reclaim them, so repeated operations can cause unbounded process memory growth and denial of service. Forward union, intersection, non-tuple operand elements, and pure-Python builds are not affected by this reference leak. This issue is fixed in version 6.9.1.