FreeBSD Security Advisory

FreeBSD Security Advisories security-advisories at
Fri Jan 4 17:04:50 PST 2002


FreeBSD-SA-02:02                                            Security Advisory
                                                                FreeBSD, Inc.

Topic:          pw(8) race condition may allow disclosure of master.passwd

Category:       core
Module:         pw
Announced:      2002-01-04
Credits:        ryan beasley <ryanb at>
Affects:        All releases prior to 4.5-RELEASE,
                4.4-STABLE prior to the correction date
Corrected:      2001-12-21 15:21:32 UTC (4.4-STABLE aka RELENG_4)
                2001-12-21 15:22:55 UTC (4.4-RELEASEp1 aka RELENG_4_4)
                2001-12-21 15:23:04 UTC (4.3-RELEASEp21 aka RELENG_4_3)
FreeBSD only:   YES

I.   Background

The pw(8) utility is used to create, remove, modify, and display system
users and groups.

II.  Problem Description

When creating, removing, or modifying system users, the pw utility
modifies the system password file `/etc/master.passwd'.  This file
contains the users' encrypted passwords and is normally only readable
by root.  During the modification, a temporary copy of the file is
created. However, this temporary file is mistakenly created with
permissions that allow it to be read by any user.

III. Impact

A local attacker can read the temporary file created by pw(8) and
use the encrypted passwords to conduct an off-line dictionary attack.
A successful attack would result in the recovery of one or more
passwords.  Because the temporary file is short-lived (it is removed
almost immediately after creation), this can be difficult to exploit:
an attacker must `race' to read the file before it is removed.

IV.  Workaround

1) Do not use pw(8) to create, remove, or modify system users.

V.   Solution

One of the following:

1) Upgrade your vulnerable FreeBSD system to 4-STABLE (RELENG_4), the
4.4-RELEASE security-fix branch (RELENG_4_4), or the 4.3-RELEASE
security-fix branch (RELENG_4_3), dated after the correction date.

2) FreeBSD 4.x systems prior to the correction date:

The following patch has been verified to apply to FreeBSD 4.3-RELEASE,
4.4-RELEASE, and 4-STABLE dated prior to the correction date.  This
patch may or may not apply to older, unsupported releases of FreeBSD.

Download the patch and the detached PGP signature from the following
locations, and verify the signature using your PGP utility.

Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch
# cd /usr/src/usr.sbin/pw
# make depend && make all install

VI.  Correction details

The following list contains the $FreeBSD$ revision numbers of each
file that was corrected in the FreeBSD source

Path                                                             Revision
- -------------------------------------------------------------------------
  HEAD (CURRENT)                                                     1.18
  RELENG_4 (4-STABLE)                                  
  RELENG_4_4 (4.4-RELEASE security branch)         
  RELENG_4_3 (4.3-RELEASE security branch)         
- -------------------------------------------------------------------------
Version: GnuPG v1.0.6 (FreeBSD)
Comment: For info see


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