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From: FreeBSD Security Advisories (security-advisoriesFreeBSD.org)
Date: Mon Mar 12 2001 - 17:47:59 CST

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    =============================================================================
    FreeBSD-SA-01:29 Security Advisory
                                                                    FreeBSD, Inc.

    Topic: rwhod allows remote denial of service

    Category: core
    Module: rwhod
    Announced: 2001-03-12
    Credits: Mark Huizer <xaaxaa.iae.nl>
    Affects: All released versions of FreeBSD 3.x, 4.x.
                    FreeBSD 3.5-STABLE prior to the correction date.
                    FreeBSD 4.2-STABLE prior to the correction date.
    Corrected: 2000-12-23 (FreeBSD 3.5-STABLE)
                    2000-12-22 (FreeBSD 4.2-STABLE)
    FreeBSD only: NO

    I. Background

    rwhod(8) is a server which implements the rwho protocol, which
    communicates information on system uptime and logged-in users between
    machines on a network.

    II. Problem Description

    Malformed packets sent to the rwhod daemon could cause it to crash,
    thereby denying service to clients if rwhod is not run under a
    watchdog process which causes it to automatically restart in the event
    of a failure. The rwhod daemon is not run in this way in the default
    invocation from /etc/rc.conf using the rwhod_enable variable.

    All versions of FreeBSD 3.x and 4.x prior to the correction date
    including 3.5.1-RELEASE and 4.2-RELEASE are vulnerable to this
    problem, if they have been configued to run rwhod (this is not enabled
    by default).

    III. Impact

    Remote users can cause the rwhod daemon to crash, denying service to
    clients.

    IV. Workaround

    Implement packet filtering at perimeter firewalls or on the local
    machine using ipfw(8)/ipf(8) to prevent untrusted users from
    connecting to the rwhod service. The rwhod daemon listens on UDP port
    513 by default.

    V. Solution

    Upgrade your vulnerable FreeBSD system to 3.5-STABLE or 4.2-STABLE
    after the respective correction dates.

    To patch your present system: download the relevant patch from the
    below location, and execute the following commands as root:

    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:29/rwhod.patch
    # fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-01:29/rwhod.patch.asc

    This patch has been verified to apply to FreeBSD 4.2-RELEASE and
    FreeBSD 3.5.1-RELEASE. It may or may not apply to older releases.

    Verify the detached PGP signature using your PGP utility.

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

    Kill and restart rwhod to cause the changes to take effect. If you
    have started rwhod with non-standard options (e.g. by setting
    rwhod_flags in /etc/rc.conf) then the below command will need to be
    modified appropriately.

    # killall -KILL rwhod
    # /usr/sbin/rwhod

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