User-controlled header names and values containing newlines can allow injecting HTTP headers.
Exploitability
AV:NAC:LAT:PPR:HUI:NVulnerable System
VC:NVI:HVA:NSubsequent System
SC:NSI:NSA:N5.9/CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:NInput Validation