documentclass{beamer}
usetheme{Warsaw}
usepackage{tikz}


makeatletter
setbeamertemplate{footline}{%
  leavevmode%
  hbox{begin{beamercolorbox}[wd=.5paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm plus1fill,rightskip=.3cm]{author in head/foot}%
    usebeamerfont{author in head/foot}insertshortauthor
  end{beamercolorbox}%
  begin{beamercolorbox}[wd=.5paperwidth,ht=2.5ex,dp=1.125ex,leftskip=.3cm,rightskip=.3cm plus1fil]{title in head/foot}%
    usebeamerfont{title in head/foot}insertshorttitle
  end{beamercolorbox}}%
  vskip0pt%
begin{tikzpicture}[overlay, remember picture]
    draw[color=green, line width=0.2cm] (current page.south west) rectangle (current page.north east);
end{tikzpicture}
}
makeatother

begin{document}

begin{frame}
Test
end{frame}

end{document}