In conjunction with data injection, this situation can allow injection of data into arbitrary files, for example, /etc/passwd. On its own, file injection can be used to create files and directories with which the attacker's chosen names can be used in future attacks. For example, the attacker could force an application to create a file with sensitive information on a world-readable location.

Klocwork security vulnerability (SV) checkers identify calls that create potentially dangerous data; these calls are considered unsafe sources. An unsafe source can be any data provided by the user, since the user could be an attacker or has the potential for introducing human error.

Mitigation and prevention

Validate all user data for allowable lexical values and size. For example, if usernames have to be part of the directory structure, check them for size and content on alphanumeric characters.

Example 1

16     protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
17         String name = req.getParameter("userName");
18         File userDir = new File("userFiles", name);
19         File profile = new File(userDir, "profile");
20         FileOutputStream stream = new FileOutputStream(profile);
21         try {
22             createFileWithSensitiveInformation(stream);
23         } finally {
24             stream.close();
25         }
26     }

SV.PATH.INJ is reported for line 20: 'name' contains data coming from an HTTP request parameter and might be tainted (line 17). This value is used to create file 'profile' on line 19 which is used on line 20 to create a FileOutputStream. This can be used to inject information into an arbitrary file in the server file system.

Security guidelines

Extension

This checker can be extended through the Klocwork knowledge base. See Tuning Java analysis for more information.