WatchGuard Fireware allows user enumeration, e.g., in the Firebox XML-RPC login handler. A login request that contains a blank password sent to the XML-RPC agent in Fireware v11.12.1 and earlier returns different responses for valid and invalid usernames. An attacker could exploit this vulnerability to enumerate valid usernames on an affected Firebox.
watchguardsupport.force.com/publicKB?type=KBSecurityIssues&SFDCID=kA62A0000000KlGSAU
packetstormsecurity.com/files/142177/watchguardfbxtm-xxeinject.txt
www.sidertia.com/Home/Community/Blog/2017/04/17/Fixed-the-Fireware-Vulnerabilities-discovered-by-Sidertia
www.watchguard.com/support/release-notes/fireware/11/en-US/EN_ReleaseNotes_Fireware_11_12_2/index.html