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Security checks based on untrusted sources can be bypassed. The Any untrusted object or parameter should argument must be defensively copied before the a security check is performed. The copy operation must be a deep copy; the implementation of the clone() method may produce a shallow copy, which can still be compromised. In addition, the implementation of the clone() method can be provided by the attacker . See guidelines MET08-J. Do not use the clone method to copy untrusted method parameters and FIO00(see OBJ06-J. Defensively copy mutable inputs and mutable internal components for more information).

Noncompliant Code Example

This noncompliant code example describes a security vulnerability from the JDK Java 1.5 .0 java.io package. In this release, java.io.File was non-final is nonfinal, allowing an attacker to supply an untrusted parameter argument constructed by extending the legitimate java.io.File class. In this manner, the getPath() method can be overridden so that the security check passes the first time it is called but the value changes the second time to refer to a sensitive file such as /etc/passwd. This is an example of a time-of-check-, time-of-use (TOCTOU) vulnerability.

public RandomAccessFile openFile(final java.io.File f) {
  askUserPermission(f.getPath());
  // ...
  return (RandomAccessFile)AccessController.doPrivileged(new PrivilegedAction <Object>() {
    public Object run() {
      return new RandomAccessFile(f, f.getPath());
    }
  });
}

The attacker can could extend java.io.File as follows:

public class BadFile extends java.io.File {
  private int count;
  public String getPath() {
    return (++count == 1) ? "/tmp/foo" : "/etc/passwd";
  }
}

Compliant Solution (Final)

This vulnerability can be mitigated by declaring java.io.File final.

Compliant Solution (Copy)

This compliant solution ensures that the java.io.File object can be trusted . First, its reference is declared to be final preventing an attacker from modifying the reference to substitute a different object. Second, the despite not being final. The solution creates a new java.io.File object using the standard java.io.File constructor. This technique ensures that any methods invoked on the File object are the standard library methods rather than and not overriding methods potentially that have been provided by the attacker.

public RandomAccessFile openFile(java.io.File f) {
  final java.io.File copy = new java.io.File(f.getPath());
  askUserPermission(copy.getPath());
  // ...
  return (RandomAccessFile)AccessController.doPrivileged(new PrivilegedAction <Object>() {
    public Object run() {
      return new RandomAccessFile(copy, copy.getPath());
    }
  });
}

Note that using the clone() method instead of the openFile() method would copy the attacker's class, which is not desirable . (Refer to guideline MET08(see OBJ06-J. Do not use the clone method to copy untrusted method parameters.)Defensively copy mutable inputs and mutable internal components).

Risk Assessment

Basing security checks on untrusted sources can result in the check being bypassed.

Automated Detection

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TODO

Related Vulnerabilities

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

Related Guidelines

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Tool	Version	Checker	Description
Coverity	7.5	UNSAFE_REFLECTION	Implemented
Parasoft Jtest	Include Page Parasoft_V Parasoft_V	CERT.SEC02.TDRFL	Protect against Reflection injection

Related Guidelines

Android Implementation Details

The code examples using the java.security package are not applicable to Android, but the principle of the rule is applicable to Android apps.

Bibliography

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Image Added Image Added Image Added SEC08-J. Protect sensitive operations with security manager checks      Platform Security (SEC)      SEC10-J. Define custom security permissions for fine grained security