SuSE: kernel Local privilege escalation vulnerability

    Date25 Mar 2003
    Posted ByLinuxSecurity Advisories
    The local attacker can use ptrace and attach to a modprobe process that is spawned if the user triggers the loading of a kernel module using the kmod kernel module subsystem. The vulnerability allows the attacker to execute arbitrary commands as root.
                            SuSE Security Announcement
            Package:                kernel
            Announcement-ID:        SuSE-SA:2003:021
            Date:                   Tuesday, Mar 25 2003 18:00 MET
            Affected products:      7.1, 7.2, 7.3, 8.0, 8.1
                                    SuSE Linux Database Server,
                                    SuSE eMail Server III, 3.1
                                    SuSE Linux Enterprise Server 7,
                                    SuSE Linux Enterprise Server 8,
                                    SuSE Linux Firewall on CD/Admin host
                                    SuSE Linux Connectivity Server
                                    SuSE Linux Office Server
            Vulnerability Type:     local privilege escalation
            Severity (1-10):        6
            SuSE default package:   yes
            Cross References:       CAN-2003-0127
        Content of this advisory:
            1) security vulnerability resolved: kernel
               problem description, discussion, solution and upgrade information
            2) pending vulnerabilities, solutions, workarounds:
               - none in this security announcement
            3) standard appendix (further information)
    1)  problem description, brief discussion, solution, upgrade information
        The Linux kernel has a security flaw in all versions used on SuSE
        products excluding the upcoming SuSE Linux 8.2 distribution. The flaw
        is known as ptrace/modprobe bug: The local attacker can use ptrace and
        attach to a modprobe process that is spawned if the user triggers the
        loading of a kernel module using the kmod kernel module subsystem.
        This can be done by asking for network protocols that are supplied by
        kernel modules which are not loaded (yet). The vulnerability allows
        the attacker to execute arbitrary commands as root.
        There exists a temporary workaround against this flaw: It is possible
        to temporaryly disable the kmod kernel module loading subsystem in the
        kernel after all necessary kernel modules have been loaded (Note: SuSE
        systems do not unload kernel modules in regular intervals.). If the
        temporary workaround is chosen, it should be made sure that no
        additional kernel modules need to be loaded afterwards (such as ISDN
        drivers, scsi subsystem drivers or filesystem drivers such as the
        iso9660 filesystem for cdroms and the language codepages).
        To disable the kmod kernel module loading subsystem, use the following
        command as root:
          echo /no/such_file > /proc/sys/kernel/modprobe
        If this command is inserted into a boot script that runs after all
        services in a runlevel have been launched, it is an efficient
        permanent solution.
        This workaround can be reverted by writing the original content
        ("/sbin/modprobe") back to the /proc/sys/kernel/modprobe file.
        Please note that it is still possible for the root user to manually
        load kernel modules.
        As a permanent remedy for the problem we offer kernel update packages
        for download from our ftp server. Please follow the guidelines that
        are given in the extensive installation intructions below. The update
        should be performed with special care in order to make sure that the
        system will properly boot after the package update.
        Note: Managing the necessary patches, building and mostly testing
        kernel update packages is an extremely worksome and therefore also
        time-consuming process. SuSE wishes to provide the same quality and
        reliability in update packages as customers are used to from the
        shipped original products. Even though our kernel updates are
        thoroughly tested, the numerous possible hardware configurations for the
        x86 platform give a certain probability for a functional failure of
        parts of the kernel after the update has been performed. Some of the
        possible failures cannot be handled by SuSE by definition. These
        include (and are not limited to) possible problems with NVIDIA chipset
        graphics boards that make use of hardware 3D acceleration. SuSE cannot
        deliver the binary only driver for the NVIDIA graphics boards in the
        kernel RPM.
        The kernel of a Linux system is the most critical component with respect
        to stability, reliability and security. By consequence, an update of that
        component requires some care and full attention to succeed. If you do
        not run a system where multiple users have access to, you may want to
        consinder to not perform this update since the security risk imposed
        by this bug is very small on a system with only one user.
        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, seperated 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 family processors
          k_orig    # kernel built with unmodified sources
          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.
        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 
        where  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
      **** 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.
      **** 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.
        Download sources for all kernel RPM packages:
        Our maintenance customers are being notified individually. The packages
        are being offered to install from the maintenance web.
    2)  Pending vulnerabilities in SuSE Distributions and Workarounds:
      - there are no items listed in this security announcements.
    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
           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 This email address is being protected from spambots. You need JavaScript enabled to view it.),
           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 
           to verify the signature of the package, where  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 "This email address is being protected from spambots. You need JavaScript enabled to view it." 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 .
      - SuSE runs two security mailing lists to which any interested party may
        This email address is being protected from spambots. You need JavaScript enabled to view it.
            -   general/linux/SuSE security discussion.
                All SuSE security announcements are sent to this list.
                To subscribe, send an email to
                    <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        This email address is being protected from spambots. You need JavaScript enabled to view it.
            -   SuSE's announce-only mailing list.
                Only SuSE's security announcements are sent to this list.
                To subscribe, send an email to
                    <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        For general information or the frequently asked questions (faq)
        send mail to:
            <This email address is being protected from spambots. You need JavaScript enabled to view it.> or
            <This email address is being protected from spambots. You need JavaScript enabled to view it.> respectively.
        SuSE's security contact is <This email address is being protected from spambots. You need JavaScript enabled to view it.> or <This email address is being protected from spambots. You need JavaScript enabled to view it.>.
        The <This email address is being protected from spambots. You need JavaScript enabled to view it.> 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 <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    pub  1024D/9C800ACA 2000-10-19 SuSE Package Signing Key <This email address is being protected from spambots. You need JavaScript enabled to view it.>
    Version: GnuPG v1.0.6 (GNU/Linux)
    Comment: For info see
    Roman Drahtmüller,
    SuSE Security.
     -                                                                      -
    | Roman Drahtmüller      <This email address is being protected from spambots. You need JavaScript enabled to view it.> // "You don't need eyes to see, |
      SuSE Linux AG - Security       Phone: //             you need vision!"
    | Nürnberg, Germany     +49-911-740530 //           Maxi Jazz, Faithless |
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