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  • [FreeBSD-Announce] FreeBSD Security Advisory FreeBSD-SA-19:12.telnet

    From FreeBSD Security Advisories@21:1/5 to All on Tue Aug 13 05:48:35 2019
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    ============================================================================= FreeBSD-SA-19:12.telnet Security Advisory
    The FreeBSD Project

    Topic: telnet(1) client multiple vulnerabilities

    Category: contrib
    Module: contrib/telnet
    Announced: 2019-07-24
    Credits: Juniper Networks
    Affects: All supported versions of FreeBSD.
    Corrected: 2019-07-19 15:37:29 UTC (stable/12, 12.0-STABLE)
    2019-07-24 12:51:52 UTC (releng/12.0, 12.0-RELEASE-p8)
    2019-07-19 15:27:53 UTC (stable/11, 11.2-STABLE)
    2019-07-24 12:51:52 UTC (releng/11.2, 11.2-RELEASE-p12)
    2019-07-24 12:51:52 UTC (releng/11.3, 11.3-RELEASE-p1)
    CVE Name: CVE-2019-0053

    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

    The telnet(1) command is a TELNET protocol client, used primarily to
    establish terminal sessions across a network.

    II. Problem Description

    Insufficient validation of environment variables in the telnet client
    supplied in FreeBSD can lead to stack-based buffer overflows. A stack-
    based overflow is present in the handling of environment variables when connecting via the telnet client to remote telnet servers.

    This issue only affects the telnet client. Inbound telnet sessions to telnetd(8) are not affected by this issue.

    III. Impact

    These buffer overflows may be triggered when connecting to a malicious
    server, or by an active attacker in the network path between the client
    and server. Specially crafted TELNET command sequences may cause the
    execution of arbitrary code with the privileges of the user invoking
    telnet(1).

    IV. Workaround

    Do not use telnet(1) to connect to untrusted machines or over an
    untrusted network.

    V. Solution

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

    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

    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-19:12/telnet.patch
    # fetch https://security.FreeBSD.org/patches/SA-19:12/telnet.patch.asc
    # gpg --verify telnet.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>.

    VI. Correction details

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

    Branch/path Revision
    - ------------------------------------------------------------------------- stable/12/ r350139 releng/12.0/ r350281 stable/11/ r350140 releng/11.2/ r350281 releng/11.3/ r350281
    - -------------------------------------------------------------------------

    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-2019-0053>

    The latest revision of this advisory is available at <URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-19:12.telnet.asc> -----BEGIN PGP SIGNATURE-----

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