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A web shell is a web security threat, which is a web-based implementation of the shell concept. No command-line environment is required on either the host or the client. A web shell could be programmed in any language that the target server supports. NETPythonPerlRuby and Unix shell scripts are also used, although not as common because it is not very common for web servers to support these languages. Using network monitoring tools such as Wiresharkan attacker can find vulnerabilities which are exploited resulting in a web shell installation.
These vulnerabilities may be present in content management system applications or the web server 's software. An attacker can use a web shell to issue commands, perform privilege escalation on the web server, and the ability to uploaddeletedownload and execute files on the web server. Web shells are used in attacks mostly because they are multi-purpose and are difficult to detect. Web shells are installed through vulnerabilities in web application or weak server security configuration including the following:  .
An attacker may also modify spoof the Content-Type header to be sent by the attacker in a file upload to bypass improper file validation validation using MIME type sent by the clientwhich will result in a successful upload of the attacker's shell. Web shells can be as short as just one line of code. The following example PHP script is 15 bytes in size:. If an attacker inserts this line of code into a malicious file with a PHP filename extension such as.
This attack could have been prevented if the file permissions did not allow viewing the file or if the shell functions of PHP were disabled so that arbitrary shell commands cannot be executed from PHP.
Other malicious actions are able to be executed by attackers with that web shell, such as replacing the contents of a file on the web server.
For example, consider the following command:. The above command could be used to replace the contents of the index. Attackers can also use the Bash command rm to delete files on the web server and mv to move files. A web shell is usually installed by taking advantage of vulnerabilities present in the web server's software.
That is why removal of these vulnerabilities are important to avoid the potential risk of a compromised web server. The following are security measures for preventing the installation of a web shell:  .
Web shells can be easily modified, so it's not easy to detect web shells and antivirus software are often not able to detect web shells. The following are common indicators that a web shell is present on a web server:  . For example, a file generating suspicious traffic e. Web shells may also contain a login form, which is often disguised as an error page.A web shell is a piece of code that written to get control over a web server. It is helpful for post exploitation attacks.
We can use a web shell to maintain access to the server. There are various types of shells. Some web shells provide a reverse connection while others give a bind connection. A known example for a web shell is c Also there is a great tool called weevly that allow you to create a PHP shell quickly.
Using weevly you can do various things such as set a password to shell, run multiple commands, encrypt the script etc. In this document we are going to see how we can develop a very basic web shell. This shell is for a PHP environment. So we can use PHP to code it. Before we continue let's understand some theories.
The primary goal of a web shell is to run some given commands on the server. In PHP there are several functions such as systemexec etc to accomplish this task. Both of system and exec function do the same. These functions get a valid unix command as the argument and execute it on the server.
The system function will print the result while exec function don't print. If we want to get the output of exec function we can use echo command.
Now it is time to start building our script. Hear is the PHP script that we are using to make a back door on the server. This code will fetch the http GET parameter called 'cmd' and put it as a argument for exec function.
Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. As stated by Luke you need to use a server side language, like php. This is a really simple php example:. Save this as myfilename. The same thing can be accomplished with asp, java, ruby, python, Just make a file script. You can return the user to the original page with header:.
Learn more. Run a shell script with an html button Ask Question. Asked 8 years, 10 months ago.
Active 1 year, 5 months ago. Viewed k times. I want to launch a bash script when a button is pressed on a website. Any suggestions? Mat What about the case of running the script on the user's machine? Active Oldest Votes.
This answer works on my Ubuntu desktop with apache2 and php5 installed.
Web Shell PHP Exploit 💀 What, Why & How To Fix
Following is some additional information to help better understand this answer: 1. PHP is likely the easiest. This is really just an expansion of BBB's answer which lead to to get my experiment working.
This requires 3 files. Could you please expand on the need for? Maybe it can be removed? There is a tutorial given over here.This alert describes the frequent use of web shells as an exploitation vector. Web shells can be used to obtain unauthorized access and can lead to wider network compromise. This alert outlines the threat and provides prevention, detection, and mitigation strategies.
Consistent use of web shells by Advanced Persistent Threat APT and criminal groups has led to significant cyber incidents. The detection and mitigation measures outlined in this document represent the shared judgement of all participating agencies.
A web shell is a script that can be uploaded to a web server to enable remote administration of the machine. Infected web servers can be either Internet-facing or internal to the network, where the web shell is used to pivot further to internal hosts.
A web shell can be written in any language that the target web server supports. Perl, Ruby, Python, and Unix shell scripts are also used.
Using network reconnaissance tools, an adversary can identify vulnerabilities that can be exploited and result in the installation of a web shell. For example, these vulnerabilities can exist in content management systems CMS or web server software. Once successfully uploaded, an adversary can use the web shell to leverage other exploitation techniques to escalate privileges and to issue commands remotely.
These commands are directly linked to the privilege and functionality available to the web server and may include the ability to add, delete, and execute files as well as the ability to run shell commands, further executables, or scripts. Web shells are frequently used in compromises due to the combination of remote access and functionality. Even simple web shells can have a considerable impact and often maintain minimal presence. While a web shell itself would not normally be used for denial of service DoS attacks, it can act as a platform for uploading further tools, including DoS capability.
Web shells such as China Chopper, WSO, C99 and BK are frequently chosen by adversaries; however these are just a small number of known used web shells. Web shells can be delivered through a number of web application exploits or configuration weaknesses including:.
The above tactics can be and are combined regularly. For example, an exposed admin interface also requires a file upload option, or another exploit method mentioned above, to deliver successfully. A successfully uploaded shell script may allow a remote attacker to bypass security restrictions and gain unauthorized system access.
Installation of a web shell is commonly accomplished through web application vulnerabilities or configuration weaknesses. Therefore, identification and closure of these vulnerabilities is crucial to avoiding potential compromise. The following suggestions specify good security and web shell specific practices:. Due to the potential simplicity and ease of modification of web shells, they can be difficult to detect. For example, anti-virus products sometimes produce poor results in detecting web shells.
The following may be indicators that your system has been infected by a web shell.I'm thinking that this coupled with Middler of Airpwn two wireless cards would make a fantastic local attack.
That's a great idea Stewart. As long as we can successfully inject our JS in to the target session, Shell of the Future can be used for taking over it. Very nice job indeed. This is help proving the possible effects of XSS. Great Tool, But lava 1 Will it also work without any problem if there is some firewall or anything in between the client browser and the attackers public page.
Thomas Thanks : Amar Thanks buddy! Ans: 1 As long as the victim can reach the attacker's web server this will work. The limitations are: 1 If you inject code in www.
This is due to Same Origin Policy. Lava: I'm getting the following error: Unable to start server, exiting application. Reason: The process cannot access the file because it is being used by another process. It isn't, I also restarted the box and same error. CodeCritter There could be two reasons: 1 Because you are running the tool as a normal user. Try running it as administrator or set the server port to something greater than instead of the default value of Change the server port to something else and it should fix it.
I get the JS script properly loaded and logged into the Sotfconsole, however clicking the link just brings me to the website, no banner, no control. From what I understand you are able to hijack the session but the hijacked session does not display a banner like it should. The reason this could be happening is because the URL ends with '. So Shell of the Future is fetching this page directly from the server instead of routing it through the victim. If this is the case then make suitable changes to the direct-fetch configuration and it should work.
The 'Hijack Session' link is meant to be the way you explained. When you click the link Shell of the Future sets the victim ID in a cookie and starts tunneling your session. Hopefully this should resolve the issue, please let me know if it doesn't.
Client side XSS is not a serious problem.Attracting more than a half-million annual readers, this is the security community's go-to destination for technical breakdowns of the latest threats, critical vulnerability disclosures and cutting-edge research. First appearances may be deceiving Web attackers have have been using a method of stashing pieces of their PHP backdoor exploit code within the meta-data headers of these image files to evade detections. This is not a completely new tactic however it is not as well known by the defensive community so we want to raise awareness.
Let's first take a quick look at why this technique is being utlized by attackers. Here is a graphic taken from this years Trustwave SpiderLabs Global Security Report that lists the top malicious file types uploaded to compromised web servers:.
Let's take a look at a standard obfuscated R57 shell example:. Once PHP executes this code, it will decode and inflate the data stream and the result will be a basic file uploader webshell similar to the following:. These types of attacks and compromises are so prevalent in Shared Hosting environments where end users do not properly update their web application software. In response to these types of scenarios, Hosting Provider security teams often employ OS-level back-end processes that scan the local file systems looking for tell-tale signs of webshell backdoor code.
One example tool is called MalDetect. This script can be run to analyze files and detect various forms of malicious code. If we run maldetect against our example R57 webshell file we get the following:. As you can see, maldetect identified this PHP file with of of its generic base64 injection signatures.
While this indivudual file scanning does work, for managability, most organizations opt to run maldetect as part of an ogoing automated process run through scheduling tools such as Cron. The big problem with this process is that, for performance reasons, many organizations opt to only scan PHP files and exclude other file types from being scanned This brings us back to the beginning of the blog post.
Due to the cleanup tactics used by most organizations, the bad guys had to figure out a method of hiding their backdoor code in places that most likely would not be inspected. In this case, we are talking about hiding PHP code data within the Exif image header fields. The concept of Stegonography is not new and there have been many past examples of its use for passing data, however we are now seeing it used for automated code execution.
I do want to give a proper hat-tip to the Sucuri Research Team who also found similar techniques being employed. If you were to view-source in a browser or use something like the unix strings command, you could see the new code added to the top of the image files:.
This data does not in any way interfere with the proper rendering of the image file itself. It is used extensivly in many different plugins and tools. Here is an example from Facebook's GitHub Repo:. This code checks to see if there is a POST request body named "zz1" and if there is, it will then eval the contents.
We can not accurately estimate how widespread this technique is being used however there is a small amount of empirical evidence by simply using public search engines to flag any web pages that list characteristics of either EXIF code hiding or searching for this specific base64 encoded string value. There are hundreds of examples of this base64 encoded data being present within image files.
As this scenario shows, attackers can take advantage of your excluded content to hide their code. This is a bot-free zone. Please check the box to let us know you're human.
Download Now. Read complimentary reports and insightful stories in the Trustwave Resource Center. Looks Can Be Deceiving Do any of these pictures look suspicious?How to hack websites with PHP Shells
Here is a graphic taken from this years Trustwave SpiderLabs Global Security Report that lists the top malicious file types uploaded to compromised web servers: Let's take a look at a standard obfuscated R57 shell example: Notice the Base64 encoded parameter data and then the PHP Eval call at the end. Once PHP executes this code, it will decode and inflate the data stream and the result will be a basic file uploader webshell similar to the following: Incident Response Steps - Identification and Eradication These types of attacks and compromises are so prevalent in Shared Hosting environments where end users do not properly update their web application software.This popularity is due in particular to the great personalization offered by themes and extensions.
A web shell can be written in any language supported by the target web server. Perl, Python, Ruby, and Unix shell scripts are also used. A web — shell itself cannot attack or exploit a remote vulnerabilityso it is always the second step of an attack.
Using network discovery tools, an adversary can identify vulnerabilities that can be exploited and result in the installation of a web shell. For example, these vulnerabilities may exist in content management systems CMS or Web server software.
Once the download is successful, an opponent can use the web shell to exploit other operating techniques to scale privileges and issue commands remotely. These commands are directly related to the privileges and features available on the Web server and may include the ability to add, execute, and delete files, also has the ability to execute shell commands, additional executable scripts.
Web shells are frequently used in trade offs because of the combination of remote access and features. Even simple web hulls can have a huge impact and often maintain a minimal presence.
Single Line PHP Script to Gain Shell
A web shell exploit usually contains a backdoor that allows an attacker to remotely access and possibly control a server at any time. This would prevent the attacker from having to exploit a vulnerability whenever access to the compromised server is required. An attacker can also choose to repair the vulnerability themselves, to ensure that no one else exploits this vulnerability.
In this way, the attacker can keep a low profile and avoid any interaction with an administrator, while obtaining the same result. It should also be noted that many popular Web shells use password authentication and other techniques to ensure that only the attacker downloading the web shell has access to it. Most web shells also contain code to identify and prevent search engines from listing the shell and, therefore, blacklisting the domain or server hosting the web application.
With access to the root account, the attacker can essentially do everything on the system, including, changing WordPress file and folder permissionsinstalling software, adding and removing users, stealing passwords, reading e-mails, etc. Useful Resource: Getting shell after admin access in WordPress site.
Another use of Web-Shells is to integrate servers into a botnet. A botnet is a network of arbitrated systems that an attacker would control, either to use oneself or to be rented to other criminals. This configuration is commonly used in distributed denial of service DDoS attackswhich require significant bandwidth. In this case, the attacker has no interest in harming or stealing anything from the system on which the web shell was deployed.
Instead, they will simply use their resources whenever necessary. Although a web shell is not normally used for WordPress DDoS attackit can serve as a platform for downloading other tools, including the DoS feature. Web shells can be delivered through a number of Web application exploits or configuration weaknesses, including:. The tactics above can be combined regularly.