SEC34-J. Do not allow tainted variables in doPrivileged blocks

It is important to disallow operations on tainted inputs in a doPrivileged() block. This is because an adversary may supply malicious input that may result in privilege escalation attacks.

Noncompliant Code Example

This noncompliant code example accepts a tained filename argument. An adversary may supply the name of a sensitive password file, complete with the path and consequently force operations to be performed on the wrong file.

private void privilegedMethod(final String filename) throws FileNotFoundException {
  try {
    FileInputStream fis = (FileInputStream) AccessController.doPrivileged(
      new PrivilegedExceptionAction() {
        public FileInputStream run() throws FileNotFoundException {
          return new FileInputStream(filename);            
        }
      }
    );
    // do something with the file and then close it
  } catch (PrivilegedActionException e) { 
    // forward to handler and log 
  }
}

Compliant Solution

This compliant solution explicitly hardcodes the name of the file and confines the variables used in the privileged block to the same method. This ensures that no malicious file can be loaded by exploiting the privileges of the corresponding code.

private void privilegedMethod() throws FileNotFoundException {
  try {
    FileInputStream fis = (FileInputStream) AccessController.doPrivileged(
      new PrivilegedExceptionAction() {
        public FileInputStream run() throws FileNotFoundException {
          return new FileInputStream("/usr/home/filename");            
        }
      }
    );
    // do something with the file and then close it
  } catch (PrivilegedActionException e) { 
    // forward to handler and log 
  }
}

Risk Assessment

Allowing tainted inputs in privileged operations can lead to privilege escalation attacks.

Automated Detection

TODO

Related Vulnerabilities

Search for vulnerabilities resulting from the violation of this rule on the CERT website.

References

[[API 06]] method doPrivileged()
[[Gong 03]] Sections 6.4, AccessController and 9.5 Privileged Code
[[SCG 07]] Guideline 6-1 Safely invoke java.security.AccessController.doPrivileged
[[MITRE 09]] CWE ID 266 "Incorrect Privilege Assignment", CWE ID 272 "Least Privilege Violation"

SEC33-J. Do not expose standard APIs that use the immediate caller's class loader instance to untrusted code      02. Platform Security (SEC)      03. Declarations and Initialization (DCL)