Webmin before 2.640 does not safely construct a filename for saving of an attachment within the mailboxes component. This occurs in mailboxes/detachall.cgi.
Exploitability
AV:NAC:LAT:NPR:LUI:NVulnerable System
VC:HVI:HVA:HSubsequent System
SC:HSI:HSA:H9.4/CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:HOther