The resolve_redirects function in sessions.py in requests 2.1.0 through 2.5.3 allows remote attackers to conduct session fixation attacks via a cookie without a host value in a redirect.
Exploitability
AV:NAC:MAu:NImpact
C:PI:PA:P6.8/AV:N/AC:M/Au:N/C:P/I:P/A:P