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FullDisclosure: SuSE Security Announcement: Kernel brk() vulnerability (SuSE-SA:2003:049)

From: Olaf Kirch (okir_at_suse.de)
Date: Dec 04 2003



                        SUSE Security Announcement

        Package: Linux Kernel
        Announcement-ID: SuSE-SA:2003:049
        Date: Thursday, December 4th 2003 15:30 MET
        Affected products: 7.3, 8.0, 8.1, 8.2, 9.0
                                SuSE Linux Enterprise Server 7,
                                SuSE Linux Database Server,
                                SuSE eMail Server III, 3.1
                                SuSE Linux Firewall on CD/Admin host
                                SuSE Linux Office Server
                                SuSE Linux Desktop 1.0
                                SuSE Linux School Server
        Vulnerability Type: local root exploit
        Severity (1-10): 8
        SUSE default package: yes
        Cross References: CAN-2003-0961

    Content of this advisory:
        1) security vulnerability resolved:
           - Linux kernel brk() integer overflow
           problem description, discussion, solution and upgrade information
        2) pending vulnerabilities, solutions, workarounds:
             - KDE
             - mc
             - apache1/2
             - freeradius
             - screen
             - mod_gzip
             - unace

        3) standard appendix (further information)


1) problem description, brief discussion, solution, upgrade information

    This security update fixes a serious vulnerability in the Linux
    kernel. A missing bounds check in the brk() system call allowed
    processes to request memory beyond the maximum size allowed for tasks,
    causing kernel memory to be mapped into the process' address space.
    This allowed local attackers to obtain super user privileges.

    An exploit for this vulnerability is circulating in the wild, and
    has been used to compromise OpenSource development servers.

    There is no temporary workaround for this bug.

    This update also fixes several other security issues in the

     - race condition with files opened via O_DIRECT which could
        be exploited to read disk blocks randomly. This could include
        blocks of previously deleted files with sensitive content.
     - don't allow users to send signals to kmod
     - when reading the RTC, don't leak kernel stack data to user space

    The following paragraphs will guide you through the installation
    process in a step-by-step fashion. The character sequence "****"
    marks the beginning of a new paragraph. In some cases, you decide
    if the paragraph is needed for you or not. Please read through all
    of the steps down to the end. All of the commands that need to be
    executed are required to be run as the superuser (root). Each step
    relies on the steps before to complete successfully.

  **** Step 1: Determine the needed kernel type

    Please use the following command to find the kernel type that is
    installed on your system:

      rpm -qf /boot/vmlinuz

    The following options are possible (disregarding the version and build
    number following the name, separated by the "-" character):

      k_deflt # default kernel, good for most systems.
      k_i386 # kernel for older processors and chipsets
      k_athlon # kernel made specifically for AMD Athlon(tm) family processors
      k_psmp # kernel for Pentium-I dual processor systems
      k_smp # kernel for SMP systems (Pentium-II and above)

  **** Step 2: Download the package for your system

    Please download the kernel RPM package for your distribution with the
    name starting as indicated by Step 1. The list of all kernel rpm
    packages is appended below. Note: The kernel-source package does not
    contain any binary kernel in bootable form. Instead, it contains the
    sources that the binary kernel rpm packages are made from. It can be
    used by administrators who have decided to build their own kernel.
    Since the kernel-source.rpm is an installable (compiled) package that
    contains sources for the linux kernel, it is not the source RPM for
    the kernel RPM binary packages.

    The kernel RPM binary packages for the distributions can be found at these
    locations below ftp://ftp.suse.com/pub/suse/i386/update/.


    After downloading the kernel RPM package for your system, you should
    verify the authenticity of the kernel rpm package using the methods as
    listed in section 3) of each SUSE Security Announcement.

  **** Step 3: Installing your kernel rpm package

    Install the rpm package that you have downloaded in Steps 3 or 4 with
    the command
        rpm -Uhv --nodeps --force <K_FILE.RPM>
    where <K_FILE.RPM> is the name of the rpm package that you downloaded.

    Warning: After performing this step, your system will likely not be
             able to boot if the following steps have not been fully

    If you run SUSE LINUX 8.1 and haven't applied the previous
    kernel update (SUSE-SA:2003:034), AND use the freeswan package,
    you also need to update the freeswan rpm as a dependency as offered
    by YOU (Yast Online Update). The package can be downloaded from

  **** Step 4: configuring and creating the initrd

    The initrd is a ramdisk that is being loaded into the memory of your
    system together with the kernel boot image by the bootloader. The
    kernel uses the content of this ramdisk to execute commands that must
    be run before the kernel can mount its actual root filesystem. It is
    usually used to initialize scsi drivers or NIC drivers for diskless

    The variable INITRD_MODULES (set in the files /etc/rc.config up to
    7.3) or /etc/sysconfig/kernel (after and including 8.0)) determines
    which kernel modules will be loaded in the initrd before the kernel
    has mounted its actual root filesystem. The variable should contain
    your scsi adapter (if any) or filesystem driver modules.

    With the installation of the new kernel, the initrd has to be
    re-packed with the update kernel modules. Please run the command


    as root to create a new init rmadisk (initrd) for your system.
    On SuSE Linux 8.1 and later, this is done automatically when the
    RPM is installed.

  **** Step 5: bootloader

    If you have a 7.x system, you must now run the command


    as root to initialize the lilo bootloader for your system. Then
    proceed to the next step.

    If you run a SUSE LINUX 8.x or a SLES8 system, there are two options:
    Depending on your software configuration, you have the lilo bootloader
    or the grub bootloader installed and initialized on your system.
    The grub bootloader does not require any further actions to be
    performed after the new kernel images have been moved in place by the
    rpm Update command.
    If you have a lilo bootloader installed and initialized, then the lilo
    program must be run as root. Use the command

      grep LOADER_TYPE /etc/sysconfig/bootloader

    to find out which boot loader is configured. If it is lilo, then you
    must run the lilo command as root. If grub is listed, then your system
    does not require any bootloader initialization.

    Warning: An improperly installed bootloader may render your system

  **** Step 6: reboot

    If all of the steps above have been successfully applied to your
    system, then the new kernel including the kernel modules and the
    initrd should be ready to boot. The system needs to be rebooted for
    the changes to become active. Please make sure that all steps are
    complete, then reboot using the command
        shutdown -r now
        init 6

    Your system should now shut down and reboot with the new kernel.

    Our maintenance customers are being notified individually. The packages
    are being offered to install from the maintenance web.

    Intel i386 Platform:

    patch rpm(s):
    source rpm(s):

    patch rpm(s):
    source rpm(s):

    patch rpm(s):
    source rpm(s):

    patch rpm(s):
    source rpm(s):


    Opteron x86_64 Platform:

    patch rpm(s):
    source rpm(s):


2) Pending vulnerabilities in SUSE Distributions and Workarounds:

    - KDE
    New KDE packages are currently being tested. These packages fixes
    several vulnerabilities:
      + remote root compromise (CAN-2003-0690)
      + weak cookies (CAN-2003-0692)
      + SSL man-in-the-middle attack
      + information leak through HTML-referrer (CAN-2003-0459)
      + wrong file permissions of config files
    The packages will be release as soon as testing is finished.

    - mc
    By using a special combination of links in archive-files it is possible
    to execute arbitrary commands while mc tries to open it in its VFS.
    The packages are currently tested and will be release as soon as

    - apache1/2
    The widely used HTTP server apache has several security vulnerabilities:
      - locally exploitable buffer overflow in the regular expression code.
        The attacker must be able to modify .htaccess or httpd.conf.
        (affects: mod_alias and mod_rewrite)
      - under some circumstances mod_cgid will output its data to the
        wrong client (affects: apache2)
    Update packages are available on our FTP servers.

    - freeradius
    Two vulnerabilities were found in the FreeRADIUS package.
    The remote denial-of-service attack bug was fixed and new packages
    will be released as soon as testing was successfully finished.
    The other bug is a remote buffer overflow in the module rlm_smb.
    We do not ship this module and will fix it for future releases.

    - screen
    A buffer overflow in screen was reported. Since SuSE Linux 8.0
    we do not ship screen with the s-bit anymore. An update package
    will be released for 7.3 as soon as possible.

    - mod_gzip
    The apache module mod_gzip is vulnerable to remote code execution
    while running in debug-mode. We do not ship this module in debug-mode
    but future versions will include the fix.

    - unace
    The tool unace for handling the archive format ACE is vulnerable to
    a buffer overflow that can be triggered with long file-names as command
    line argument. This only affects unace version 2.5. Unfortunately this
    tool is provided closed source only from the author. Therefore we are
    unable to check for other bugs or look at the patch.
    Update packages are available from our FTP servers.


3) standard appendix: authenticity verification, additional information

  - Package authenticity verification:

    SUSE update packages are available on many mirror ftp servers all over
    the world. While this service is being considered valuable and important
    to the free and open source software community, many users wish to be
    sure about the origin of the package and its content before installing
    the package. There are two verification methods that can be used
    independently from each other to prove the authenticity of a downloaded
    file or rpm package:
    1) md5sums as provided in the (cryptographically signed) announcement.
    2) using the internal gpg signatures of the rpm package.

    1) execute the command
        md5sum <name-of-the-file.rpm>
       after you downloaded the file from a SUSE ftp server or its mirrors.
       Then, compare the resulting md5sum with the one that is listed in the
       announcement. Since the announcement containing the checksums is
       cryptographically signed (usually using the key security_at_suse.de),
       the checksums show proof of the authenticity of the package.
       We disrecommend to subscribe to security lists which cause the
       email message containing the announcement to be modified so that
       the signature does not match after transport through the mailing
       list software.
       Downsides: You must be able to verify the authenticity of the
       announcement in the first place. If RPM packages are being rebuilt
       and a new version of a package is published on the ftp server, all
       md5 sums for the files are useless.

    2) rpm package signatures provide an easy way to verify the authenticity
       of an rpm package. Use the command
        rpm -v --checksig <file.rpm>
       to verify the signature of the package, where <file.rpm> is the
       filename of the rpm package that you have downloaded. Of course,
       package authenticity verification can only target an un-installed rpm
       package file.
        a) gpg is installed
        b) The package is signed using a certain key. The public part of this
           key must be installed by the gpg program in the directory
           ~/.gnupg/ under the user's home directory who performs the
           signature verification (usually root). You can import the key
           that is used by SUSE in rpm packages for SUSE Linux by saving
           this announcement to a file ("announcement.txt") and
           running the command (do "su -" to be root):
            gpg --batch; gpg < announcement.txt | gpg --import
           SUSE Linux distributions version 7.1 and thereafter install the
           key "build_at_suse.de" upon installation or upgrade, provided that
           the package gpg is installed. The file containing the public key
           is placed at the top-level directory of the first CD (pubring.gpg)
           and at ftp://ftp.suse.com/pub/suse/pubring.gpg-build.suse.de .

  - SUSE runs two security mailing lists to which any interested party may

        - general/linux/SUSE security discussion.
            All SUSE security announcements are sent to this list.
            To subscribe, send an email to

        - SUSE's announce-only mailing list.
            Only SUSE's security announcements are sent to this list.
            To subscribe, send an email to

    For general information or the frequently asked questions (faq)
    send mail to:
        <suse-security-info_at_suse.com> or
        <suse-security-faq_at_suse.com> respectively.

    SUSE's security contact is <security_at_suse.com> or <security_at_suse.de>.
    The <security_at_suse.de> public key is listed below.

    The information in this advisory may be distributed or reproduced,
    provided that the advisory is not modified in any way. In particular,
    it is desired that the clear-text signature shows proof of the
    authenticity of the text.
    SUSE Linux AG makes no warranties of any kind whatsoever with respect
    to the information contained in this security advisory.

Type Bits/KeyID Date User ID
pub 2048R/3D25D3D9 1999-03-06 SuSE Security Team <security_at_suse.de>
pub 1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <build_at_suse.de>

Version: GnuPG v1.0.6 (GNU/Linux)
Comment: For info see http://www.gnupg.org


- --
  Thomas Biege <thomas_at_suse.de>, SUSE LINUX AG, Security Support & Auditing
   "lynx -source http://www.suse.de/~thomas/contact/thomas.asc | pgp -fka"
     Key fingerprint = 51 AD B9 C7 34 FC F2 54 01 4A 1C D4 66 64 09 83
- --
        ... stay with me, safe and ignorant, go back to sleep...
                                - Maynard James Keenan

Version: GnuPG v1.0.7 (GNU/Linux)


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