User-controlled data URLs parsed by urllib.request.DataHandler allow injecting headers through newlines in the data URL mediatype.
Exploitability
AV:NAC:LAT:PPR:LUI:NVulnerable System
VC:NVI:HVA:NSubsequent System
SC:NSI:LSA:N6/CVSS:4.0/AV:N/AC:L/AT:P/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:L/SA:NOther