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[Jamie Strandboge <jamie@xxxxxxxxxx>]

** Also affects: lightdm (Ubuntu)
   Importance: Undecided
       Status: New

** Also affects: lightdm (Ubuntu Oneiric)
   Importance: Undecided
       Status: New

** Changed in: lightdm (Ubuntu Oneiric)
   Importance: Undecided => High

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https://bugs.launchpad.net/bugs/834079

Title:
  files written as root to user-controlled folders

Status in Light Display Manager:
  Triaged
Status in “lightdm” package in Ubuntu:
  New
Status in “lightdm” source package in Oneiric:
  New
Status in “lightdm” package in Debian:
  Confirmed

Bug description:
  Hey,

  as you were on CC: I guess you're already aware, but reporting so it
  can be tracked upstream.

  Short version: http://seclists.org/oss-sec/2011/q3/393

  Long version: .dmrc and Xauthority files are written by lightdm
  running as root while they're in user controlled folders. An user can,
  via a symlink, overwrite root-owned files. It doesn't look like it can
  achieve easily privilege-escalation (since the content is quite fixed)
  but it's still bad.

  Basically the correct fix seems to have workers process which would
  setuid() to the user before writing content to those files.

  There's no CVE affected yet.

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