#Java get file path without name fullIn the example above, the absolute path contains the full path to the file and not only the file name as seen in the non absolute path. #Java get file path without name windowsUnfortunately, the canonicalization is performed after the validation, which renders the validation ineffective.Path differences in Windows Windows absolute path C:\Windows\calc.exe Windows non absolute path (relative path) calc.exe The getCanonicalFile() method behaves like getCanonicalPath() but returns a new File object instead of a String. sequences to break out of the specified directory when the validate() method is present. For example, the path /img/./etc/passwd resolves to /etc/passwd. The getCanonicalPath() method throws a security exception when used in applets because it reveals too much information about the host machine. ) are also removed so that the input is reduced to a canonicalized form before validation is carried out. #Java get file path without name codeThis noncompliant code example attempts to mitigate the issue by using the File.getCanonicalPath() method, introduced in Java 2, which fully resolves the argument and constructs a canonicalized path. Special file names such as dot dot (. Noncompliant Code Example ( getCanonicalPath()) The path name of the link might appear to reside in the /img directory and consequently pass validation, but the operation will actually be performed on the final target of the link, which can reside outside the intended directory.įileOutputStream fis = new FileOutputStream(file) An attacker can also create a link in the /img directory that refers to a directory or file outside of that directory. However, the user can still specify a file outside the intended directory by entering an argument that contains. Do not operate on files in shared directories. The program also uses the isInSecureDir() method defined in FIO00-J. By prepending /img/ to the directory, this code enforces a policy that only files in this directory should be opened. This noncompliant code example allows the user to specify the path of an image file to open. Normalize strings before validating them. This recommendation is a specific instance of IDS01-J. If the referenced file is in a secure directory, then, by definition, an attacker cannot tamper with it and cannot exploit the race condition. Do not operate on files in shared directories for more information). The canonical path name can be used to determine whether the referenced file name is in a secure directory (see FIO00-J. Fortunately, this race condition can be easily mitigated. While the canonical path name is being validated, the file system may have been modified and the canonical path name may no longer reference the original valid file. A path equivalence vulnerability occurs when an attacker provides a different but equivalent name for a resource to bypass security checks.Ĭanonicalization contains an inherent race window between the time the program obtains the canonical path name and the time it opens the file. A directory traversal vulnerability allows an I/O operation to escape a specified operating directory. Frequently, these restrictions can be circumvented by an attacker by exploiting a directory traversal or path equivalence vulnerability. Validation may be necessary, for example, when attempting to restrict user access to files within a particular directory or to otherwise make security decisions based on the name of a file name or path name. Consequently, all path names must be fully resolved or canonicalized before validation. Further, the textual representation of a path name may yield little or no information regarding the directory or file to which it refers. More than one path name can refer to a single directory or file. In addition to these specific issues, a wide variety of operating system–specific and file system–specific naming conventions make validation difficult.Ĭanonicalizing file names makes it easier to validate a path name. " refers to the directory's parent directory. Inside a directory, the special file name ". Path names may also contain special file names that make validation difficult: For example, the final target of a symbolic link called trace might be the path name /home/system/trace. These file links must be fully resolved before any file validation operations are performed. A relative pathname, in contrast, must be interpreted in terms of information taken from some other pathname.Ībsolute or relative path names may contain file links such as symbolic (soft) links, hard links, shortcuts, shadows, aliases, and junctions. An absolute pathname is complete in that no other information is required to locate the file that it denotes. According to the Java API for class java.io.File:Ī pathname, whether abstract or in string form, may be either absolute or relative.
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