Jakub Wilk discovered that the dpkg-source component of dpkg, the Debian package management system, doesn't correctly handle paths in patches of source packages, which could make it traverse directories. Raphaël Hertzog additionally discovered that symbolic links in the .pc directory are followed, which could make it traverse directories too.
Both issues only affect source packages using the "3.0 quilt" format at unpack-time.
For the stable distribution (lenny), these problems have been fixed in version 1.14.31.
For the testing (squeeze) and unstable distributions (sid), these problems will be fixed soon.
We recommend that you upgrade your dpkg packages.
Further information about Debian Security Advisories, how to apply these updates to your system and frequently asked questions can be found at: https://www.debian.org/security/