Relative Path Traversal
The product uses external input to construct a pathname that should be within a restricted directory, but it does not properly neutralize sequences such as ".." that can resolve to a location that is outside of that directory.
This allows attackers to traverse the file system to access files or directories that are outside of the restricted directory.
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 URLs are vulnerable to this attack:
A simple way to execute this attack is like this:
The following code could be for a social networking application in which each user's profile information is stored in a separate file. All files are stored in a single directory.
While the programmer intends to access files such as "/users/cwe/profiles/alice" or "/users/cwe/profiles/bob", there is no verification of the incoming user parameter. An attacker could provide a string such as:
The program would generate a profile pathname like this:
When the file is opened, the operating system resolves the "../" during path canonicalization and actually accesses this file:
As a result, the attacker could read the entire text of the password file.
Notice how this code also contains an error message information leak (CWE-209) if the user parameter does not produce a file that exists: the full pathname is provided. Because of the lack of output encoding of the file that is retrieved, there might also be a cross-site scripting problem (CWE-79) if profile contains any HTML, but other code would need to be examined.
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 file handling.
Weaknesses in this category are related to the A01 category "Broken Access Control" in the OWASP Top Ten 2021.
This category identifies Software Fault Patterns (SFPs) within the Path Traversal cluster (SFP16).
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