rpc.py through 0.6.0 allows Remote Code Execution because an unpickle occurs when the "serializer: pickle" HTTP header is sent. In other words, although JSON (not Pickle) is the default data format, an unauthenticated client can cause the data to be processed with unpickle.
Exploitability
AV:NAC:LPR:NUI:NScope
S:UImpact
C:HI:HA:H9.8/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H