Vulnerable Systems:
* Canonical Ubuntu Linux 10.04 LTS
* Canonical Ubuntu Linux 11.04
* Canonical Ubuntu Linux 11.10
* Canonical Ubuntu Linux 12.04 LTS i386
* Canonical Ubuntu Linux 12.04 LTS amd64
add-apt-repository can add PPAs and automatically import the PPA gpg key.Unfortunately, it uses apt-key, which in turn uses gpg to download the key from a keyserver.gpg downloads keys from keyservers using the short key id, which is trivial to collide.It is therefore possible to either MITM the point where gpg downloads the key from the keyserver, or to simply upload a second colliding key to the keyserver. This can result in being able to MITM packages installed from PPAs.