Unrestricted Upload of File with Dangerous Type
The software allows the attacker to upload or transfer files of dangerous types that can be automatically processed within the product's environment.
The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.
Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.
The following code intends to allow a user to upload a picture to the web server. The HTML code that drives the form on the user end has an input field of type "file".
Once submitted, the form above sends the file to upload_picture.php on the web server. PHP stores the file in a temporary location until it is retrieved (or discarded) by the server side code. In this example, the file is moved to a more permanent pictures/ directory.
The problem with the above code is that there is no check regarding type of file being uploaded. Assuming that pictures/ is available in the web document root, an attacker could upload a file with the name:
Since this filename ends in ".php" it can be executed by the web server. In the contents of this uploaded file, the attacker could use:
Once this file has been installed, the attacker can enter arbitrary commands to execute using a URL such as:
which runs the "ls -l" command - or any other type of command that the attacker wants to specify.
The following code demonstrates the unrestricted upload of a file with a Java servlet and a path traversal vulnerability. The action attribute of an HTML form is sending the upload file request to the Java servlet.
When submitted the Java servlet's doPost method will receive the request, extract the name of the file from the Http request header, read the file contents from the request and output the file to the local upload directory.
This code does not perform a check on the type of the file being uploaded (CWE-434). This could allow an attacker to upload any executable file or other file with malicious code.
Additionally, the creation of the BufferedWriter object is subject to relative path traversal (CWE-23). Since the code does not check the filename that is provided in the header, an attacker can use "../" sequences to write to files outside of the intended directory. Depending on the executing environment, the attacker may be able to specify arbitrary files to write to, leading to a wide variety of consequences, from code execution, XSS (CWE-79), or system crash.
Weaknesses in this category are related to the A04 "Insecure Design" category in the OWASP Top Ten 2021.
Weaknesses in this category are related to the CISQ Quality Measures for Security. Presence of these weaknesses could reduce the security of the software.
Weaknesses in this category are related to the CISQ Quality Measures for Security, as documented in 2016 with the Automated Source Code Security Measure (ASCSM) Specif...
This view (slice) covers all the elements in CWE.
CWE entries in this view are listed in the 2020 CWE Top 25 Most Dangerous Software Weaknesses.
This view outlines the SMM representation of the Automated Source Code Data Protection Measurement specifications, as identified by the Consortium for Information & So...