APT before 0.8.15.2 does not properly validate inline GPG signatures, which allows man-in-the-middle attackers to install modified packages via vectors involving lack of an initial clearsigned message.
Exploitability
AV:NAC:MAu:NImpact
C:NI:PA:N4.3/AV:N/AC:M/Au:N/C:N/I:P/A:N