It was discovered that APT, the high level package manager, does not properly invalidate unauthenticated data (CVE-2014-0488), performs incorrect verification of 304 replies (CVE-2014-0487), does not perform the checksum check when the Acquire::GzipIndexes option is used (CVE-2014-0489) and does not properly perform validation for binary packages downloaded by the apt-get download command (CVE-2014-0490).
For the stable distribution (wheezy), these problems have been fixed in version 0.9.7.9+deb7u3.
For the unstable distribution (sid), these problems have been fixed in version 1.0.9.
We recommend that you upgrade your apt packages.