NetBSD Security Advisory 2009-004: NetBSD OpenPAM passwd(1) changing weakness

[NetBSD Security Officer <security-officer%NetBSD.org@localhost>]

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                 NetBSD Security Advisory 2009-004
                 =================================

Topic:          NetBSD OpenPAM passwd(1) changing weakness

Version:        NetBSD-current:         affected before June 14, 2009
                NetBSD 5.0:             affected
                NetBSD 4.0.1:           affected
                NetBSD 4.0:             affected

Severity:       Change root password as normal user

Fixed:          NetBSD-current:         June 14, 2009
                NetBSD-5-0 branch:      June 18, 2009
                        (5.0.1 will include the fix)
                NetBSD-5 branch:        June 18, 2009
                        (5.1 will include the fix)
                NetBSD-4-0 branch:      June 18, 2009
                        (4.0.2 will include the fix)
                NetBSD-4 branch:        June 18, 2009
                        (4.1 will include the fix)


Please note that NetBSD releases prior to 4.0 are no longer supported.
It is recommended that all users upgrade to a supported release.


Abstract
========

A verification weakness in the pam_unix module allows an authenticated
attacker with knowledge of the current root password to reset it.


Technical Details
=================

The pam_unix authentication module provided by NetBSD does not verify
the user invoking a password change properly. This allows an
authenticated, unprivileged user to change the root password, given
the old root password.

Authentication as root is typically limited to members of a special
group called "wheel" in order to limit the impact of a leaked root
password. For this reason, the ability of changing the root password
is traditionally limited to users who have already authenticated as
root.

Please note that this only affects systems using normal UNIX password
authentication.


Solutions and Workarounds
=========================

In order to verify if you are affected by the problem, look for a line
in /etc/pam.d/system stating

        password        required        pam_unix.so     no_warn try_first_pass

If such a line exists, invoke the command

        passwd root

as a regular user. If the command issues the error "Unable to change
auth token: permission denied", the system is not affected.

A temporary workaround is to add the line

        password        prerequisite    pam_group.so    no_warn group=wheel 
fail_safe

before the pam_unix line to /etc/pam.d/system. This allows only members
of the wheel group to change passwords until the issue can be addressed.
Note however that this can increase the time user accounts are
compromised in case of a security incident.

For all NetBSD versions, you need to obtain the fixed NetBSD sources and
rebuild and install the new PAM libraries.

The fixed source may be obtained from the NetBSD CVS repository.
The following instructions briefly summarize how to upgrade your PAM
libraries by updating your source tree and rebuilding and installing
a new version of them.

* NetBSD-current:

        Systems running NetBSD-current dated from before 2009-06-15
        should be upgraded to NetBSD-current dated 2009-06-16 or later.

        The following directories need to be updated from the
        netbsd-current CVS branch (aka HEAD):
                lib/libpam/modules/pam_unix

        To update from CVS, re-build, and re-install pam_unix:
                # cd src
                # cvs update -d -P lib/libpam/modules/pam_unix
                # cd lib/libpam/modules/pam_unix
                # make USETOOLS=no cleandir dependall
                # make USETOOLS=no install

* NetBSD 5.*:

        Systems running NetBSD 5.* sources dated from before
        2009-05-17 should be upgraded from NetBSD 5.* sources dated
        2009-05-18 or later.

        The following directories need to be updated from the
        netbsd-5 or netbsd-5-0 CVS branch:
                lib/libpam/modules/pam_unix

        To update from CVS, re-build, and re-install pam_unix:

                # cd src
                # cvs update -d -P -r <branch_name> lib/libpam/modules/pam_unix
                # cd lib/libpam/modules/pam_unix
                # make USETOOLS=no cleandir dependall
                # make USETOOLS=no install

* NetBSD 4.*:

        Systems running NetBSD 4.* sources dated from before
        2009-05-17 should be upgraded from NetBSD 4.* sources dated
        2009-05-18 or later.

        The following directories need to be updated from the
        netbsd-4 or netbsd-4-0 CVS branch:
                lib/libpam/modules/pam_unix

        To update from CVS, re-build, and re-install pam_unix:

                # cd src
                # cvs update -d -P -r <branch_name> lib/libpam/modules/pam_unix
                # cd lib/libpam/modules/pam_unix
                # make USETOOLS=no cleandir dependall
                # make USETOOLS=no install


Thanks To
=========

Thomas Getzke for discovering the vulnerability, Hubert Feyrer for
reporting the vulnerability and testing the patches, and Tonnerre
Lombard for providing the fix.


Revision History
================

        2009-06-22      Initial release


More Information
================

Advisories may be updated as new information becomes available.
The most recent version of this advisory (PGP signed) can be found at 
  ftp://ftp.NetBSD.org/pub/NetBSD/security/advisories/NetBSD-SA2009-004.txt.asc

Information about NetBSD and NetBSD security can be found at
http://www.NetBSD.org/ and http://www.NetBSD.org/Security/.


Copyright 2009, The NetBSD Foundation, Inc.  All Rights Reserved.
Redistribution permitted only in full, unmodified form.

$NetBSD: NetBSD-SA2009-004.txt,v 1.1 2009/06/22 19:31:01 tonnerre Exp $

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