If the value passed to os.path.expandvars() is user-controlled a performance degradation is possible when expanding environment variables.
Exploitability
AV:LAC:LAT:PPR:HUI:NVulnerable System
VC:NVI:NVA:LSubsequent System
SC:NSI:NSA:N1.8/CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N