[Bug 1911791] Re: Openscap can report false positives

[Eduardo Barretto]

** Patch added: "bionic.debdiff"
   https://bugs.launchpad.net/ubuntu/+source/openscap/+bug/1911791/+attachment/5453537/+files/bionic.debdiff

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Title:
  Openscap can report false positives

Status in openscap package in Ubuntu:
  In Progress
Status in openscap source package in Xenial:
  In Progress
Status in openscap source package in Bionic:
  In Progress
Status in openscap source package in Focal:
  In Progress
Status in openscap source package in Groovy:
  In Progress
Status in openscap source package in Hirsute:
  In Progress

Bug description:
  [Impact]

  Openscap didn't implement Debian package version comparison algorithm.
  This can cause a user/client to get false positive results when running
  oscap.

  For example, we have a system running Bionic, with package "foo" version
  1.2.3-4ubuntu1~18.04.1 installed. Ubuntu fixed CVE-2020-XXXX on Bionic for
  "foo" on version 1.2.3-4ubuntu1. If oscap compares both version it would
  would return "false", meaning that "foo" is not vulnerable, which is not
  correct as 1.2.3-4ubuntu1 is greater than the installed version
  1.2.3-4ubuntu1~18.04.1.

  $ dpkg --compare-versions 1.2.3-4ubuntu1 gt 1.2.3-4ubuntu1~18.04.1 && echo TRUE || echo FALSE
  TRUE

  If a client relies on software like openscap to decide when to upgrade
  their system (especially for clients that need to have a downtime to
  upgrade packages), openscap could be giving the wrong information and
  causing unnecessary downtimes, or even showing the system as
  vulnerable, when it isn't or vice-versa.

  [Test Case]

  Attached to this bug is a zip file that contains oval data for 3 different
  packages (gdcm, gnutls28 and openssl) with specific CVE data for each (
  CVE-2016-5300, CVE-2018-10845 and CVE-2020-1968). This data* is for Bionic
  only.

  The test consists of comparing the installed version of the mentioned
  packages, to different versions where the CVE could have been fixed.

  For more info on the test data see:
  https://pastebin.ubuntu.com/p/cVp2xcq9fs/

  Testing procedure (Bionic):
  $ sudo apt update
  $ sudo apt install libopenscap8
  $ sudo apt install libgdcm2.8 openssl libgnutls30
  $ tar -xzf test-data.tar.gz
  $ cd test-data/
  $ ./run.sh

  Here is a diff between the results of the test, between current openscap
  and the openscap with the algorithm fix:
  https://pastebin.ubuntu.com/p/38N8GsgZnf/

  *PS: This data doesn't reflect the reality of those vulnerabilities and it
  should only be used for test purposes.

  [Where problems could occur]

  The patches only touch the comparison algorithm, so any regressions
  that it might have, might impact the comparison, generating false
  positives too.

  [Other Info]

  This affects all releases of Ubuntu, from Xenial to Hirsute.

  The versioning algorithm implemented is based on dpkg's algorithm.

  Upstream accepted and merged the Debian version comparison algorithm to
  its maint-1.3 branch and it should make it to 1.3.5 version whenever it
  gets released.

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