DistUpgrade/DistUpgradeFetcherCore.py in Update Manager before 1:0.87.31.1, 1:0.134.x before 1:0.134.11.1, 1:0.142.x before 1:0.142.23.1, 1:0.150.x before 1:0.150.5.1, and 1:0.152.x before 1:0.152.25.5 on Ubuntu 8.04 through 11.10 does not verify the GPG signature before extracting an upgrade tarball, which allows man-in-the-middle attackers to (1) create or overwrite arbitrary files via a directory traversal attack using a crafted tar file, or (2) bypass authentication via a crafted meta-release file.