SuSE: 'shadow/pam-modules' Privilege escalation vulnerability

    Date16 May 2002
    CategorySuSE
    1856
    Posted ByLinuxSecurity Advisories
    The SuSE Security Team discovered a vulnerability that allows local attackers to destroy the contents of these files or to extend the group privileges of certain users. This is possible by setting evil filesize limits before invoking one of the programs modifying the system files.
    
    ______________________________________________________________________________
    
                            SuSE Security Announcement
    
            Package:                shadow/pam-modules
            Announcement-ID:        SuSE-SA:2002:017
            Date:                   Thu May 16 12:00:00 MEST 2002
            Affected products:      8.0
            Vulnerability Type:     local privilege escalation
            Severity (1-10):        5
            SuSE default package:   yes
            Other affected systems: No.
    
        Content of this advisory:
            1) security vulnerability resolved: write() disruption in shadow utils
               problem description, discussion, solution and upgrade information
            2) pending vulnerabilities, solutions, workarounds
            3) standard appendix (further information)
    
    ______________________________________________________________________________
    
    1)  problem description, brief discussion, solution, upgrade information
    
        The shadow package contains several useful programs to maintain the
        entries in the /etc/passwd and /etc/shadow files.
            The SuSE Security Team discovered a vulnerability that allows local
        attackers to destroy the contents of these files or to extend the group
        privileges of certain users. This is possible by setting evil filesize
        limits before invoking one of the programs modifying the system files.
        Depening on the permissions of the system binaries this allows a local
        attacker to gain root privileges in the worst case. This however is not
        possible in a default installation.
            The bug has been fixed by ensuring the integrity of the data written
        to temporary files before moving them to the appropriate location of the
        system. There is no workaround so we recommend an update in any case.
        It is necessary to update the shadow package as well as the pam-modules
        package in order to prevent the truncation attacks.
    
        Please download the update package for your distribution and verify its
        integrity by the methods listed in section 3) of this announcement.
        Then, install the package using the command "rpm -Fhv file.rpm" to apply
        the update.
        Our maintenance customers are being notified individually. The packages
        are being offered to install from the maintenance web.
    
    
        i386 Intel Platform:
    
        SuSE-8.0
         ftp://ftp.suse.com/pub/suse/i386/update/8.0/a1/shadow-4.0.2-88.i386.rpm
          a4e0d03ecf7707eb7ca1f0422cae89f1
         ftp://ftp.suse.com/pub/suse/i386/update/8.0/a1/pam-modules-2002.3.9-31.i386.rpm
          70322584f014ac3e2dc2dad0beecdefb
    
        source rpm:
         ftp://ftp.suse.com/pub/suse/i386/update/8.0/zq1/shadow-4.0.2-88.src.rpm
          33af2433d9a8822202e9f6ebdc6d3e2c
         ftp://ftp.suse.com/pub/suse/i386/update/8.0/zq1/pam-modules-2002.3.9-31.src.rpm
          1bc5bbd169ffe5c35caa0a4ce681dcc0
    
    ______________________________________________________________________________
    
    2)  Pending vulnerabilities in SuSE Distributions and Workarounds:
    
        - leafnode
        The permissions of "/etc/leafnode" have been corrected. Please update
        to the newly available packages if you use leafnode.
    
        - xf86, xmodules, xloader
        Incorrect permission checks in certain X11 functions allow local attackers
        to read or write shared memory segments they should not have access to.
        Corrected packages will soon be available on 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 
           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 uninstalled rpm
           package file.
           Prerequisites:
            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 toplevel 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
        subscribe:
    
        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 annoucements 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 cleartext 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.>
    
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