[CVE-2008-4311] DBus 1.2.6

Colin Walters walters at verbum.org
Fri Dec 5 11:55:04 PST 2008

A new security release of DBus is now available:


This release contains a (partial, see below) fix for:

== Summary ==

Joachim Breitner discovered a mistake in the default configuration for the
system bus (system.conf) which made the default policy for both sent and
received messages effectively *allow*, and not deny as intended.

This release fixes the send side permission, but does not change the receive.
See below for more details.

== Available workarounds ==

Add explicit <deny> rules to existing policy files which do not
already have them.

== Mitigating factors ==

There are three important mitigating factors.

* First, in an examination of a Fedora 10 system, many services contained
explicit <deny> rules under the "default" context. These deny rules did (and
continue to) operate as expected.

* Second, an increasing trend has been for core system services to use
PolicyKit, or otherwise do security checks on the service side.  Any system
which relies on PolicyKit is unaffected by this flaw.

* Third, the SELinux DBus support is not affected by this flaw.

Now, as mentioned above this fix is partial.  DBus has two kinds of policy
permissions, send and receive.  Generally speaking, the send side permission is
much more important.  However, DBus has supported receive side permissions for
a few reasons, among those are:

* Ensuring signals containing sensitive data aren't visible by unexpected
processes.  Suggested fix: Do not put sensitive data in DBus signals; use
targeted method calls.

* A way for processes to "second-pass" filter messages before they reach their
C code.  Suggested fix: Something like PolicyKit (or just manual service-side
permission checks) remain a better way to do this.

For compatibility reasons, this release only fixes the send-side permission
check, and not receive.  A greater number of services will need to be updated
for a future tightening of the receive permission.

We are as yet unsure when (and in fact, if) the receive permission will be
tightened in the DBus 1.2 stable branch.  We will gather information about any
affected programs and make a final determination at in the near future.

== Conclusion Summary ==

* Add explicit <deny> rules under the default policy if this is applicable to
your service (i.e. not using PolicyKit or similar)
* Do not put sensitive information in signals

== Thanks ==

Thanks to Joachim Breitner for the initial report and proposed patch, Tomas
Hoger for the current fix, and others for their assistance with this issue.

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