Allowing user input to control paths used in filesystem operations may enable an attacker to access or modify otherwise protected system resources.
Path manipulation errors occur when the following two conditions are met:
- An attacker can specify a path used in an operation on the filesystem.
- By specifying the resource, the attacker gains a capability that would not otherwise be permitted. For example, the program may give the attacker the ability to overwrite the specified file or run with a configuration controlled by the attacker.
The following code uses input from an HTTP request to create a file name. The programmer has not considered the possibility that an attacker could provide a file name such as "../../tomcat/conf/server.xml", which causes the application to delete one of its own configuration files.
String rName = request.getParameter("reportName"); File rFile = new File("/usr/local/apfr/reports/" + rName); ... rFile.delete();
The following code uses input from a configuration file to determine which file to open and echo back to the user. If the program runs with privileges and malicious users can change the configuration file, they can use the program to read any file on the system that ends with the extension .txt.
fis = new FileInputStream(cfg.getProperty("sub")+".txt"); amt = fis.read(arr); out.println(arr);