• [FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-20:26.dhclient

    From FreeBSD Security Advisories@21:1/5 to All on Wed Sep 2 18:00:02 2020
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    ============================================================================= FreeBSD-SA-20:26.dhclient Security Advisory
    The FreeBSD Project

    Topic: dhclient heap overflow

    Category: core
    Module: dhclient
    Announced: 2020-09-02
    Credits: Shlomi Oberman, JSOF
    Affects: All supported versions of FreeBSD.
    Corrected: 2020-08-31 21:28:09 UTC (stable/12, 12.1-STABLE)
    2020-09-02 16:25:31 UTC (releng/12.1, 12.1-RELEASE-p9)
    2020-08-31 21:28:57 UTC (stable/11, 11.4-STABLE)
    2020-09-02 16:25:31 UTC (releng/11.4, 11.4-RELEASE-p3)
    2020-09-02 16:25:31 UTC (releng/11.3, 11.3-RELEASE-p13)
    CVE Name: CVE-2020-7461

    For general information regarding FreeBSD Security Advisories,
    including descriptions of the fields above, security branches, and the following sections, please visit <URL:https://security.FreeBSD.org/>.

    I. Background

    dhclient(8) is the default IPv4 DHCP client used on FreeBSD. It is
    responsible for contacting DHCP servers on a network segment, and for initializing and configuring network interfaces and configuring name
    resolution based on received information.

    dhclient(8) handles DHCP option 119, the Domain Search Option, which provides
    a list of domains to search when resolving names using DNS. The option data format uses a compression scheme to avoid transmitting duplicate domain name labels.

    II. Problem Description

    When parsing option 119 data, dhclient(8) computes the uncompressed domain
    list length so that it can allocate an appropriately sized buffer to store
    the uncompressed list. The code to compute the length failed to handle
    certain malformed input, resulting in a heap overflow when the uncompressed list is copied into in inadequately sized buffer.

    III. Impact

    The heap overflow could in principle be exploited to achieve remote code execution. The affected process runs with reduced privileges in a Capsicum sandbox, limiting the immediate impact of an exploit. However, it is
    possible the bug could be combined with other vulnerabilities to escape the sandbox.

    IV. Workaround

    No workaround is available. To trigger the bug, a system must be running dhclient(8) on the same network as a malicious DHCP server.

    V. Solution

    Upgrade your vulnerable system to a supported FreeBSD stable or
    release / security branch (releng) dated after the correction date, and
    restart dhclient or reboot.

    Perform one of the following:

    1) To update your vulnerable system via a binary patch:

    Systems running a RELEASE version of FreeBSD on the i386 or amd64
    platforms can be updated via the freebsd-update(8) utility:

    # freebsd-update fetch
    # freebsd-update install
    # shutdown -r +10min "Rebooting for a security update"

    2) To update your vulnerable system via a source code patch:

    The following patches have been verified to apply to the applicable
    FreeBSD release branches.

    a) Download the relevant patch from the location below, and verify the
    detached PGP signature using your PGP utility.

    # fetch https://security.FreeBSD.org/patches/SA-20:26/dhclient.patch
    # fetch https://security.FreeBSD.org/patches/SA-20:26/dhclient.patch.asc
    # gpg --verify dhclient.patch.asc

    b) Apply the patch. Execute the following commands as root:

    # cd /usr/src
    # patch < /path/to/patch

    c) Recompile the operating system using buildworld and installworld as described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

    Restart the applicable daemons, or reboot the system.

    VI. Correction details

    The following list contains the correction revision numbers for each
    affected branch.

    Branch/path Revision
    - ------------------------------------------------------------------------- stable/12/ r365010 releng/12.1/ r365257 stable/11/ r365011 releng/11.4/ r365257 releng/11.3/ r365257
    - -------------------------------------------------------------------------

    To see which files were modified by a particular revision, run the
    following command, replacing NNNNNN with the revision number, on a
    machine with Subversion installed:

    # svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

    Or visit the following URL, replacing NNNNNN with the revision number:

    <URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

    VII. References

    <URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7461>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-20:26.dhclient.asc> -----BEGIN PGP SIGNATURE-----

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