• Type: Security Hotspot Detection
    • Status: Deprecated
    • Resolution: Unresolved
    • Labels:
    • Message:
      Make sure this file handling is safe here.
    • Default Severity:
    • Impact:
    • Likelihood:
    • Covered Languages:
      C#, Java, JavaScript, PHP, VB.Net
    • Irrelevant for Languages:
      CSS, HTML, XML
    • Analysis Scope:
      Main Sources
    • Common Rule:


      Handling files is security-sensitive. It has led in the past to the following vulnerabilities:

      Any access to the file system can create a vulnerability. Exposing a file's content, path or even its existence or absence is dangerous. It is also extremely risky to create or write files without making sure that their permission and content is safe and controlled. Using a file path or reading a file content must be always done with caution as they could have been tampered with.

      The file system is a resource which can be easily exhausted. Opening too many files will use up all file descriptors, preventing other software from opening files. Filling the storage space will also prevent any additional write from happening.

      This rule flags code that initiates the use of files. The goal is to guide manual security code reviews.

      Ask Yourself Whether

      • the file or directory path you are using is coming from a user input or could have been tampered with.
      • the code exposes to an unauthorized person the existence of a file or directory. Any hint given to a user might be dangerous. The information could be given by displaying an error if the file/directory does not exist or just by returning an "Unauthorized" error when the file/directory exists but the person can't perform an action.
      • the code exposes to an unauthorized person the paths of files and/or directories, for example by listing the content of a directory and displaying the output.
      • a file or directory may be created with the wrong permissions.
      • an unvalidated user input is written into a file.
      • a file is read and its content is used without being validated.
      • a file is read and its content is exposed to an unauthorized person.
      • a file is open, created or written into each time a user performs an action.
      • files are open and not closed before executing a child process. This is only dangerous if file descriptors are inherited in your programming language (example: C, C++).

      You are at risk if you answered yes to any of those questions.

      Recommended Secure Coding Practices

      Avoid using paths provided by users or other untrusted sources if possible. If this is required, check that the path does not reference an unauthorized directory or file. See OWASP recommendations as to how to test for directory traversal. Note that the paths length should be validated too.

      No File and directory names should be exposed. They can contain sensitive information. This means that a user should not be able to list the content of unauthorized directories.

      Make sure that no attackers can test for the existence or absence of sensitive files. Knowing that a specific file exists can reveal a vulnerability or at least expose file and directory names.

      Files and directories should be created with restricted permissions and ownership. Only authorized users and applications should be able to access the files, and they should have as little permissions as needed. Modifying a file's permissions is not good enough. The permissions should be restricted from the very beginning.

      Writing user input into files should be done with caution. It could fill the storage space if the amount of data written is not controlled. It could also write dangerous data which will later be used by an application or returned to another user. This is why the user input should be validated before being written.

      Reading a file can lead to other vulnerabilities. Any file could have been modified by an attacker. Thus the same validation as for any user input should be performed on file content.

      Once a file is read, its content should only be exposed to authorized users.

      Add limits to the number of files your application access simultaneously or create because of a user action. It is possible to perform a Denial of Service attack by opening too many files, and thus exhausting available file descriptors, or by filling the file system with new files. Release file descriptors by closing files as soon as possible.
      We also recommended to have tools monitoring your system and alerting you whenever resources are nearly exhausted.

      Do not allow untrusted code to access the filesystem. For some programming languages, child-processes may have access to file descriptors opened by the parent process before the creation of the child process. This creates a vulnerability when a child process doesn't have the permission to access a file but is still able to modify it via the inherited file descriptor. Check your language documentation for "file descriptor leak" or the use of the flags O_CLOEXEC, FD_CLOEXEC, or bInheritHandles. File descriptors can be inherited in the following languages: C, C++, C#, Objective-C, Swift, Go (but disabled by default), some JVM versions, Javascript and TypeScript in Nodejs, Some PHP versions, Python, Ruby, Rust, VB6 and VB.NET.



          Issue Links

          Java RSPEC-4841 Language-Specification Active Unassigned
          C# RSPEC-4943 Language-Specification Active Unassigned
          VB.NET RSPEC-5026 Language-Specification Active Unassigned
          JavaScript RSPEC-5076 Language-Specification Active Unassigned
          PHP RSPEC-5090 Language-Specification Active Unassigned
          Python RSPEC-5222 Language-Specification Active Unassigned



              • Assignee:
                nicolas.harraudeau Nicolas Harraudeau
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