The postinst script in ppp 2.4.4rel on Debian GNU/Linux allows local users to overwrite arbitrary files via a symlink attack on the (1) /tmp/probe-finished or (2) /tmp/ppp-errors temporary file.
Improper Link Resolution Before File Access The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.