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TUCoPS :: Unix :: General :: ncurses.htm

Ncurses 4.2, 5.0 (earlier?) exploitable buffer overflows



Vulnerability

    ncurses

Affected

    ncurses 4.2, 5.0 (earlier?)

Description

    Jouko Pynnen  found following.   The CRT  screen handling  library
    ncurses  contains  buffer  overflows,  making  programs  using  it
    vulnerable.  If  the programs are  setuid or setgid,  a local user
    may  elevate  their  privilege.   The  problem  exists  in ncurses
    versions  4.2  and  5.0,  probably  earlier,  and libocurses.  The
    overflows can be exploited if the library implementation  supports
    loading of user defined terminfo files from ~/.terminfo.

    The problem has been tested and found on

        * SuSE Linux  6.4, Red Hat  Linux 6.1.  A setuid program using
          ncurses  ("cda"  in  the  xmcd  package)  was   successfully
          exploited to spawn a root shell.
        * FreeBSD,  the  program  /usr/bin/systat  is setgid and  uses
          libncurses.  An  exploit was made  which gives a  shell with
          egid=kmem.  The kmem group has read access to /dev/kmem  and
          memory of  all processes  via /proc/<pid>/mem,  and could be
          used  to   read  e.g.   crypted  or   cleartext   passwords,
          authorization  keys,  or  any  other  info  that might be in
          programs' memory space.
        * OpenBSD, having  /usr/bin/systat setgid kmem  too.  No  test
          exploit was made,  but the program  segfaults when given  an
          "evil" terminfo file.  Making  a similar exploit is probably
          possible.  This  applies to other  BSD systems as  well, but
          haven't been tested or confirmed.

    All  programs  using  ncurses  aren't necessarily vulnerable, e.g.
    "screen" is setuid root on  some systems and uses ncurses,  but it
    doesn't seem  to use  the vulnerable  functions at  least directly
    (investigated on Red Hat Linux, other systems may vary).

    When using telnet to connect  to a remote system, telnetd  on some
    platforms  doesn't  ignore  TERMINFO_DIRS  or  TERMCAP environment
    variables  (e.g.  OpenBSD).   This  means  the  problem  could  be
    remotely  exploitable  under  some  conditions  on some platforms.
    This hasn't  been confirmed  with an  exploit, however  by setting
    TERMCAP the OpenBSD telnetd can be made read any file as root.  If
    the file is something like /dev/zero, the telnetd process reads it
    infinitely until the system runs out of memory.

    The  file  ncurses/tty/lib_mvcur.c  contains  functions for moving
    around  the  cursor.   Some  of  the  functions  contain  calls to
    strcpy() without bound checking.  The target of the strcpy's is  a
    local fixed size buffer in onscreen_mvcur():

        static inline int
        onscreen_mvcur(int yold,int xold,int ynew,int xnew, bool ovw)
        /* onscreen move from (yold, xold) to (ynew, xnew) */
        {
            char        use[OPT_SIZE], *sp;


        ... a few lines later:

            sp = tparm(SP->_address_cursor, ynew, xnew);
            if (sp)
            {
                tactic = 0;
                (void) strcpy(use, sp);

    The  function  tparm()  returns   a  control  string  for   screen
    manipulation, originating  from the  terminfo file  read according
    to the environment variables TERM and TERMINFO_DIRS.  Even  though
    ncurses  implementations  on  some  platforms  reportedly   ignore
    TERMINFO_DIRS while running setuid/setgid, they check ~/.terminfo/
    for the capability files in any case.

    OPT_SIZE seems to be defined as 512. tparm() can be made return  a
    string  of   arbitrary  length   containing  arbitrary   data,  so
    exploitation is usually quite trivial.  There are a few of similar
    strcpy() calls in other functions in the file.  Many other ncurses
    functions  may  also  call  the  cursor  moving  functions   (e.g.
    endwin()) so  in order  to be  vulnerable, a  program needn't call
    mvcur().

Solution

    The authors of  ncurses and OS  vendors have been  informed over a
    week ago and they have, or will release fix packages shortly.

    A  temporary  solution  is  to  remove  the  setuid/setgid bits of
    programs using ncurses.  To check  if a program uses ncurses, type
    (on most systems):

        ldd /path/to/program

    If libncurses or  libocurses is mentioned  in the library  listing
    and the program is  setuid/setgid, then there's a  possibility for
    it to be exploited.  If 'ldd' doesn't exist on the system (or  the
    program is statically linked) you can try something like

       grep -li TERMINFO /path/to/program

    If it outputs the file path, the program probably uses ncurses  or
    derivative.  To remove the setuid/setgid bits, issue the command:

        chmod ug-s /path/to/file

    FWIW -  no version  of NetBSD  is distributed  with ncurses as the
    base curses library, it is  available in the package system  as an
    addon.  There  are no str*  calls performed on  user supplied data
    (including  the  termcap  information)  and  we  use a new termcap
    interface  that  bounds  checks   information  from  the   termcap
    entries.  An audit of the NetBSD source tree was performed in  May
    2000 to  replace the  old, unbounded,  termcap interface  with the
    updated one.

    For Caldera Systems:

      - OpenLinux Desktop 2.3
        - ftp://ftp.calderasystems.com/pub/updates/OpenLinux/2.3/current/RPMS/
        - ftp://ftp.calderasystems.com/pub/updates/OpenLinux/2.3/current/SRPMS
          * RPMS/ncurses-4.2-6.i386.rpm
          * RPMS/ncurses-devel-4.2-6.i386.rpm
          * RPMS/ncurses-devel-static-4.2-6.i386.rpm
          * RPMS/ncurses-termcap-devel-4.2-6.i386.rpm
          * RPMS/ncurses-termcap-devel-static-4.2-6.i386.rpm
          * SRPMS/ncurses-4.2-6.src.rpm

     - OpenLinux eServer 2.3 and OpenLinux eBuilder for ECential 3.0
       - ftp://ftp.calderasystems.com/pub/updates/eServer/2.3/current/RPMS/
       - ftp://ftp.calderasystems.com/pub/updates/eServer/2.3/current/SRPMS
         * RPMS/ncurses-4.2-6.i386.rpm
         * RPMS/ncurses-devel-4.2-6.i386.rpm
         * RPMS/ncurses-devel-static-4.2-6.i386.rpm
         * RPMS/ncurses-termcap-devel-4.2-6.i386.rpm
         * RPMS/ncurses-termcap-devel-static-4.2-6.i386.rpm
         * SRPMS/ncurses-4.2-6.src.rpm

     - OpenLinux eDesktop 2.4
       - ftp://ftp.calderasystems.com/pub/updates/eDesktop/2.4/current/RPMS/
       - ftp://ftp.calderasystems.com/pub/updates/eDesktop/2.4/current/SRPMS
         * RPMS/ncurses-4.2-6.i386.rpm
         * RPMS/ncurses-devel-4.2-6.i386.rpm
         * RPMS/ncurses-devel-static-4.2-6.i386.rpm
         * RPMS/ncurses-termcap-devel-4.2-6.i386.rpm
         * RPMS/ncurses-termcap-devel-static-4.2-6.i386.rpm
         * SRPMS/ncurses-4.2-6.src.rpm

    For SuSE Linux:

        ftp://ftp.suse.com/pub/suse/noarch/perms-ncurses.sh

    For FreeBSD:

        fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-00:68/ncurses.tar.gz
        fetch ftp://ftp.FreeBSD.org/pub/FreeBSD/CERT/patches/SA-00:68/ncurses.tar.gz.asc

        ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-3-stable/devel/ncurses-5.2.tgz
        ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-4-stable/devel/ncurses-5.2.tgz
        ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-4-stable/devel/ncurses-5.2.tgz
        ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/i386/packages-5-current/devel/ncurses-5.2.tgz
        ftp://ftp.FreeBSD.org/pub/FreeBSD/ports/alpha/packages-5-current/devel/ncurses-5.2.tgz

    For Red Hat:

        ftp://updates.redhat.com/6.2/alpha/ncurses-5.0-12.alpha.rpm
        ftp://updates.redhat.com/6.2/alpha/ncurses-devel-5.0-12.alpha.rpm
        ftp://updates.redhat.com/6.2/sparc/ncurses-5.0-12.sparc.rpm
        ftp://updates.redhat.com/6.2/sparc/ncurses-devel-5.0-12.sparc.rpm
        ftp://updates.redhat.com/6.2/i386/ncurses-5.0-12.i386.rpm
        ftp://updates.redhat.com/6.2/i386/ncurses-devel-5.0-12.i386.rpm
        ftp://updates.redhat.com/6.2/SRPMS/ncurses-5.0-12.src.rpm
        ftp://updates.redhat.com/7.0/i386/ncurses-5.2-2.i386.rpm
        ftp://updates.redhat.com/7.0/i386/ncurses-devel-5.2-2.i386.rpm
        ftp://updates.redhat.com/7.0/SRPMS/ncurses-5.2-2.src.rpm

    For Debian:

        http://security.debian.org/dists/potato/updates/main/source/ncurses_5.0-6.0potato1.diff.gz
        http://security.debian.org/dists/potato/updates/main/source/ncurses_5.0-6.0potato1.dsc
        http://security.debian.org/dists/potato/updates/main/source/ncurses_5.0.orig.tar.gz
        http://security.debian.org/dists/potato/updates/main/binary-all/ncurses-base_5.0-6.0potato1_all.deb
        http://security.debian.org/dists/potato/updates/main/binary-all/ncurses-term_5.0-6.0potato1_all.deb
        http://security.debian.org/dists/potato/updates/main/binary-alpha/libncurses5-dbg_5.0-6.0potato1_alpha.deb
        http://security.debian.org/dists/potato/updates/main/binary-alpha/libncurses5-dev_5.0-6.0potato1_alpha.deb
        http://security.debian.org/dists/potato/updates/main/binary-alpha/libncurses5_5.0-6.0potato1_alpha.deb
        http://security.debian.org/dists/potato/updates/main/binary-alpha/ncurses-bin_5.0-6.0potato1_alpha.deb
        http://security.debian.org/dists/potato/updates/main/binary-arm/libncurses5-dbg_5.0-6.0potato1_arm.deb
        http://security.debian.org/dists/potato/updates/main/binary-arm/libncurses5-dev_5.0-6.0potato1_arm.deb
        http://security.debian.org/dists/potato/updates/main/binary-arm/libncurses5_5.0-6.0potato1_arm.deb
        http://security.debian.org/dists/potato/updates/main/binary-arm/ncurses-bin_5.0-6.0potato1_arm.deb
        http://security.debian.org/dists/potato/updates/main/binary-i386/libncurses5-dbg_5.0-6.0potato1_i386.deb
        http://security.debian.org/dists/potato/updates/main/binary-i386/libncurses5-dev_5.0-6.0potato1_i386.deb
        http://security.debian.org/dists/potato/updates/main/binary-i386/libncurses5_5.0-6.0potato1_i386.deb
        http://security.debian.org/dists/potato/updates/main/binary-i386/ncurses-bin_5.0-6.0potato1_i386.deb
        http://security.debian.org/dists/potato/updates/main/binary-m68k/libncurses5-dbg_5.0-6.0potato1_m68k.deb
        http://security.debian.org/dists/potato/updates/main/binary-m68k/libncurses5-dev_5.0-6.0potato1_m68k.deb
        http://security.debian.org/dists/potato/updates/main/binary-m68k/libncurses5_5.0-6.0potato1_m68k.deb
        http://security.debian.org/dists/potato/updates/main/binary-m68k/ncurses-bin_5.0-6.0potato1_m68k.deb
        http://security.debian.org/dists/potato/updates/main/binary-powerpc/libncurses5-dbg_5.0-6.0potato1_powerpc.deb
        http://security.debian.org/dists/potato/updates/main/binary-powerpc/libncurses5-dev_5.0-6.0potato1_powerpc.deb
        http://security.debian.org/dists/potato/updates/main/binary-powerpc/libncurses5_5.0-6.0potato1_powerpc.deb
        http://security.debian.org/dists/potato/updates/main/binary-powerpc/ncurses-bin_5.0-6.0potato1_powerpc.deb
        http://security.debian.org/dists/potato/updates/main/binary-sparc/libncurses5-dbg_5.0-6.0potato1_sparc.deb
        http://security.debian.org/dists/potato/updates/main/binary-sparc/libncurses5-dev_5.0-6.0potato1_sparc.deb
        http://security.debian.org/dists/potato/updates/main/binary-sparc/libncurses5_5.0-6.0potato1_sparc.deb
        http://security.debian.org/dists/potato/updates/main/binary-sparc/ncurses-bin_5.0-6.0potato1_sparc.deb

    For Immunix OS:

        http://www.immunix.org/ImmunixOS/6.2/updates/RPMS/ncurses-5.0-12_StackGuard.i386.rpm
        http://www.immunix.org/ImmunixOS/6.2/updates/RPMS/ncurses-devel-5.0-12_StackGuard.i386.rpm
        http://www.immunix.org/ImmunixOS/6.2/updates/SRPMS/ncurses-5.0-12_StackGuard.src.rpm
        http://www.immunix.org/ImmunixOS/7.0-beta/updates/RPMS/ncurses-5.2-2_StackGuard.i386.rpm
        http://www.immunix.org/ImmunixOS/7.0-beta/updates/RPMS/ncurses-devel-5.2-2_StackGuard.i386.rpm
        http://www.immunix.org/ImmunixOS/7.0-beta/updates/SRPMS/ncurses-5.2-2_StackGuard.src.rpm

    For Turbo Linux:

        ftp://ftp.turbolinux.com/pub/updates/6.0/security/ncurses-5.2-2.i386.rpm
        ftp://ftp.turbolinux.com/pub/updates/6.0/security/ncurses-devel-5.2-2.i386.rpm
        ftp://ftp.turbolinux.com/pub/updates/6.0/SRPMS/ncurses-5.2-2.src.rpm


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