WEBrick 1.3.1 in Ruby 1.8.6 through patchlevel 383 1.8.7 through patchlevel 248 1.8.8dev 1.9.1 through patchlevel 376 and 1.9.2dev writes data to a log file without sanitizing non-printable characters which might allow remote attackers to modify a window's title or possibly execute arbitrary commands or overwrite files via an HTTP request containing an escape sequence for a terminal emulator.