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Date: Thu, 1 May 2014 20:52:37 -0400 (EDT)
Subject: Re: CVE request: directory traversal in DSA-2915-1-patched dpkg in Debian squeeze

Hash: SHA1

> The recent update of dpkg for CVE-2014-0471 in Debian squeeze actually
> introduces a vulnerability in that release

This is a somewhat unusual situation from the perspective of CVE
assignment. The outcome of 746306 is that C-style filenames aren't
accepted. However, we probably can't assign a CVE ID for a root cause
of "attempts to support C-style filenames," because supporting those
filenames isn't inherently unsafe if an OS vendor is programmatically,
or by policy, ensuring that the patch program is one that interacts
safely with that support.


  updated dpkg in squeeze + patch(1) from squeeze = vulnerable

behavior is something that seems to be best categorized as a release
engineering problem. Although there are very few cases in which CVE
IDs have been assigned for release engineering problems, these
problems can be within the scope of CVE, and the current one is. Use
CVE-2014-3127 for this issue. In other words, because squeeze's new
dpkg program is incompatible, in a security-relevant way, with
squeeze's patch program, the two should not have been allowed to exist
together within any correctly maintained/supported squeeze

However, there is another question that could possibly result in a
second CVE ID. On wheezy, there's apparently a security problem in, at
least, these two cases:

  1. the installed patch program is an older version of patch that's
     identical to squeeze's supported version of patch. Possibly, this
     can happen on a correctly maintained/supported Debian system
     because sometimes a system is in a partially upgraded state. In
     particular, the vulnerability affects root's use of dpkg, which
     may be a completely expected activity because the administrator
     might want to unpack a source package even though an upgrade is

  2. the patch program in root's path is not something obtained from
     Debian, e.g., the administrator intentionally decided to install
     a non-GNU patch program

We're not sure what can be done about case 1. The general issue is
that, when doing an upgrade of an arbitrary OS, the system might
intermittently be in a state in which incompatibility of
old-OS-version programs and new-OS-version programs has a major
security risk. Maybe the right answer is a policy that nobody is
allowed to do anything while an upgrade is in progress. In other
words, regular users may not be logged in, and root should only be
running the upgrade program and nothing else. ("nothing else" is
impractical; realistically, risk is reduced by running as little else
as possible.)

Case 2 possibly violates the expectations of the concept of a Linux
distribution OS or other OS. In other words, the dpkg program requires
the patch program, and therefore the administrator must ensure that
the patch program (at least, in root's path) is the one provided by
the OS vendor. If the administrator decided to install any other patch
program, the resulting security problem would typically be considered
a site-specific problem and thus outside the scope of CVE. However, a
CVE ID could be assigned of any of these is true:

  - on wheezy, dpkg doesn't have any explicit requirements about the
    patch program

  - the dpkg documentation states that a non-GNU patch program can be
    used if desired

  - Debian has a general policy that a supported program (such as
    dpkg) must be robust in the face of non-standard but reasonable
    site-specific software changes. In other words, if Debian program
    1 allows arbitrary code execution in situations where the
    administrator replaces Debian program 2 with an
    often-considered-equivalent non-Debian program, this is supposed
    to be treated as a vulnerability in Debian program 1.

- -- 
CVE assignment team, MITRE CVE Numbering Authority
M/S M300
202 Burlington Road, Bedford, MA 01730 USA
[ PGP key available through ]
Version: GnuPG v1.4.14 (SunOS)


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