In BIG-IP versions 15.0.0-15.1.0.3, 14.1.0-14.1.2.3, 13.1.0-13.1.3.3, 12.1.0-12.1.5.1, and 11.6.1-11.6.5.1, an authorized user provided with access only to the TMOS Shell (tmsh) may be able to conduct arbitrary file read/writes via the built-in sftp functionality.
