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Package Management Security on openSUSE

July 16th, 2008 by

There has been a report (with further information at this page and at the FAQ) looking at package management security on various distributions that IMO was rather condensed in its summary report and therefore raised some false alarms for various distributions including openSUSE.

Ludwig, one of our security experts, sent out a mail with a reaction to the report and I’d like to point out some of the things from the report and how it’s handled in the openSUSE 11.0 distribution.

Let me state first the major lines of defense that openSUSE uses:

  • Package downgrade is not possible, YaST will not do this automatically and therefore many of the attacks (installing an old and vulnerable package) are not possible.
  • The openSUSE download redirector serves the metadata from a known and trusted source.  I advise everybody to use the download redirector via http://download.opensuse.org.
  • The openSUSE updates have both cryptographically signed packages and cryptographically signed meta data – and YaST check these signatures and reject files that do not match the signature.

The described attacks are:

  • “Replay Attack: Metadata Replay”: Not possible since the openSUSE download redirector serves the metadata from a central location.  The only chance here would be a man-in-the-middle attack but this would not help since YaST will not do a package downgrade.
  • “Replay Attack:Mirror Control”: Yes, it’s easy to become an openSUSE mirror but this will not degrade your security since the metadata comes from the download redirector and we only redirect to mirrors that contain the right version of a package – and the redirector monitors that the mirrors contain the right files.  YaST is designed with mirrors going out of date or getting corrupted in mind.
  • Attacks called “Extraneous Dependencies”, “Unsatisfiable Dependencies”, “Provides Everything” on the other attacks page: Let me cite the page where it mentions protection against these attack: “The easiest way is to use a package manager that signs the repository metadata (like APT or YaST)”.
  • “Endless Data Attack”: This is basically a denial of service attack which the admin will soon notice and can then take appropriate action.  It cannot happen for metadata since those come from the download redirector but it could happen with openSUSE for packages since we do download the complete file and do not use the file size information contained in the metadata yet.  This is something we plan to address for our next release.

Note that when I speak about YaST I mean everything that uses the openSUSE package management library libzypp which includes YaST, zypper and the updater applets.

Note also that the FAQ has a question about the download redirector: “Q: What about OpenSUSE’s download redirector? Does it increase or decrease my security? A: OpenSUSE’s download redirector increases the user’s security…”.  I’d like to thank Christoph Thiel, Marcus Rückert and Peter Pöml for their work over the years on the redirector.  Peter is the current maintainer and did the last rewrite including the serving of metadata.

Note: if you use SUSE Linux enterprise products, then only servers owned by Novell are used via secure https connections which avoid all these attacks.

Our package management and security experts have been reviewing and improving the security aspects of the package management stack continuously – and the report shows that they were successfull.

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