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A Java OutofMemoryError occurs if when the program attempts to use more heap space than is available, even after garbage collection. Amongst others. Among other causes, this error can may result from the following:

• A memory leak (see MSC04-J. Do not leak memory)
• An infinite loop
• Limited amounts of default heap memory available
• Incorrect implementation of common data structures (hash tables, vectors, and so on)
• Unbound Unbounded deserialization
• Upon writing Writing a large number of objects to an ObjectOutputStream (see SER10-J. Avoid memory and resource leaks during serialization)
• Creating a large number of threads.
• Uncompressing a file (see IDS04-J. Safely extract files from ZipInputStream)

Some of these causes are platform-dependent and difficult to anticipate. Others, such as reading data from a file, are fairly easy to anticipate. As a result, programs must not accept untrusted input in a manner that can cause the program to exhaust memory.

Noncompliant Code Example (readLine())

This noncompliant code example places no upper bounds on the memory space required to execute the program. Consequently, the program can easily exhaust the heap.reads lines of text from a file and adds each one to a vector until a line with the word "quit" is encountered:

public class ShowHeapErrorReadNames {
  private Vector<String> names = new Vector<String>();
  private final InputStreamReader input;
  private final BufferedReader reader;

  public ReadNames(String filename) throws IOException {
    this.input = new InputStreamReaderFileReader(System.infilename);
  BufferedReader  this.reader = new BufferedReader(input);
  }

  public void addNames() throws IOException {
    while(true)try {     
      // Adding unknown number of records to a list; user can exhaust the heap
  String newName;
      while (((newName = reader.readLine()) != null) &&
    String newName = reader.readLine();
      if!(!newName.equalsIgnoreCase("quit"))) { // Enter "quit" to quit the program
        names.addElement(newName);
      } else {
    	break System.out.println("adding " + newName);
      }
    } finally {
      // Close "reader" and "input"input.close();
    }
  }

  public static void main(String[] args) throws IOException {
    ShowHeapErrorif (args.length != 1) {
      System.out.println("Arguments: [filename]");
      return;
    }
    ReadNames demo = new ShowHeapErrorReadNames(args[0]);
    demo.addNames();
  }
}

Compliant Solution

If the objects or data structures are large enough to potentially cause heap exhaustion, the programmer must consider using databases instead.

To remedy the noncompliant code example, the user can reuse a single long variable to store the input and write that value into a database containing a table User, with a field userID along with any other required fields. This prevents the heap from getting exhausted.

Noncompliant Code Example

This noncompliant code example requires more memory on the heap than is available by default. In a server-class machine using a parallel garbage collector, the default initial and maximum heap sizes are as follows for J2SE 6.0 \[[Sun 06|AA. Java References#Sun 06]\]:

• initial heap size: larger of 1/64th of the machine's physical memory on the machine or some reasonable minimum

• maximum heap size: smaller of 1/4th of the physical memory or 1GB

The code places no upper bounds on the memory space required to execute the program. Consequently, the program can easily exhaust the available heap space in two ways. First, an attacker can supply arbitrarily many lines in the file, causing the vector to grow until memory is exhausted. Second, an attacker can simply supply an arbitrarily long line, causing the readLine() method to exhaust memory. According to the Java API documentation [API 2014], the BufferedReader.readLine() method

Reads a line of text. A line is considered to be terminated by any one of a line feed ('\n'), a carriage return ('\r'), or a carriage return followed immediately by a linefeed.

Any code that uses this method is susceptible to a resource exhaustion attack because the user can enter a string of any length.

Compliant Solution (Limited File Size)

This compliant solution imposes a limit on the size of the file being read. The limit is set with the Files.size() method, which was introduced in Java SE 7. If the file is within the limit, we can assume the standard readLine() method will not exhaust memory, nor will memory be exhausted by the while loop.

class ReadNames {
  // ... Other methods and variables

  public static final int fileSizeLimit = 1000000;

  public ReadNames(String filename) throws IOException {
    long size = Files.size( Paths.get( filename));
    if (size > fileSizeLimit) {
      throw new IOException("File too large");
    } else if (size == 0L) {
      throw new IOException("File size cannot be determined, possibly too large");
    }
    this.input = new FileReader(filename);
    this.reader = new BufferedReader(input);
  }
}

Compliant Solution (Limited Length Input)

This compliant solution imposes limits both on the length of each line and on the total number of items to add to the vector. (It does not depend on any Java SE 7 or later features.)

class ReadNames {
  // ... Other methods and variables

  public static String readLimitedLine(Reader reader, int limit) 
                                       throws IOException {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < limit; i++) {
      int c = reader.read();
      if (c == -1) {
        return ((sb.length() > 0) ? sb.toString() : null);
      }
      if (((char) c == '\n') || ((char) c == '\r')) {
        break;
      }
      sb.append((char) c);
    }
    return sb.toString();
  }

  public static final int lineLengthLimit = 1024;
  public static final int lineCountLimit = 1000000;

  public void addNames() throws IOException {
    try {
      String newName;
      for (int i = 0; i < lineCountLimit; i++) {
        newName = readLimitedLine(reader, lineLengthLimit);
        if (newName == null || newName.equalsIgnoreCase("quit")) {
          break;
        }
        names.addElement(newName);
        System.out.println("adding " + newName);
      }
    } finally {
      input.close();
    }
  }

}

The readLimitedLine() method takes a numeric limit, indicating the total number of characters that may exist on one line. If a line contains more characters, the line is truncated, and the characters are returned on the next invocation. This prevents an attacker from exhausting memory by supplying input with no line breaks.

Noncompliant Code Example

In a server-class machine using a parallel garbage collector, the default initial and maximum heap sizes are as follows for Java SE 6 [Sun 2006]:

• Initial heap size: larger of 1/64 of the machine's physical memory or some reasonable minimum.
• Maximum heap size: smaller of 1/4 of the physical memory or 1GB.

This noncompliant code example requires more memory on the heap than is available by default:

/*

/** Assuming the heap size as 512 MB 
 * (calculated as 1/4th4 of 2 GB2GB RAM = 512 MB512MB)
 *  Considering long values being entered (64 bits each, 
 * the max number of elements
 *  would be 512 MB/64bits512MB/64 bits = 
 * 67108864)
 */
public class ShowHeapErrorReadNames {
  // Accepts unknown number of records
  Vector<Long> names = new Vector<Long>(); // Accepts unknown number of records
   long newID = 0L;
   int count = 67108865;
   int i = 0;
   InputStreamReader input = new InputStreamReader(System.in);
   Scanner reader = new Scanner(input);

   public void addNames() {
    try {
      do {
        // Adding unknown number of records to a list
        // The user can enter more number of IDs than what the heap can support and,
 
       // as a result, exhaust the heap. Assume that the record ID
        // is a 64 -bit long value
      
       System.out.print("Enter recordID (To quit, enter -1): ");
        newID = reader.nextLong();

       
       names.addElement(newID);
        i++;
      } while (i < count || newID != -1);
    } finally {
  // Close "reader" and "input".close();
    }
  }

   public static void main(String[] args) {
    ReadNames ShowHeapError demo = new ShowHeapErrorReadNames();
     demo.addNames();
   }
}

Compliant Solution

...

A simple compliant solution is to reduce the number of names to read:

Code Block
bgColor #ccccff
// ... int count = 10000000; // ...

Compliant Solution

The OutOfMemoryError can be avoided by ensuring the absence of infinite loops, memory leaks, and unnecessary object retention. When memory requirements are known ahead of time, the heap size can be tailored to fit the requirements using the following runtime parameters [Java 2006 Wiki MarkupThe {{OutOfMemoryError}} can be avoided by making sure that there are no infinite loops, memory leaks or unnecessary object retention. If memory requirements are known ahead of time, the heap size in Java can be tailored to fit the requirements using the following runtime parameters \[[Java 06|AA. Java References#Java 06]\]:

java -Xms<initial heap size> -Xmx<maximum heap size>

For example:,

java -Xms128m -Xmx512m ShowHeapErrorReadNames

Here the initial heap size is set to 128 MB 128MB and the maximum heap size to 512 MB512MB.

This setting These settings can be changed either using the Java Control Panel or from the command line. It They cannot be adjusted through the application itself.

Noncompliant Code Example

According to the Java API \[[API 06|AA. Java References#API 06]\], Class {{ObjectInputStream}} documentation:

ObjectOutputStream and ObjectInputStream can provide an application with persistent storage for graphs of objects when used with a FileOutputStream and FileInputStream respectively. ObjectInputStream is used to recover the objects previously serialized. Other uses include passing objects between hosts using a socket stream or for marshaling and unmarshaling arguments and parameters in a remote communication system.

By design, only the first time an object is written, does it get reflected in the stream. Subsequent writes write a handle to the object into the stream. A table mapping the objects written to the stream to the corresponding handle is also maintained. Because of this handle, references that may not persist during normal runs of the program are also retained. This can cause an OutOfMemoryError when streams remain open for extended durations.

FileOutputStream fos = new FileOutputStream("data.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(new Date());
// ... 

Compliant Solution (3)

If heap related issues arise, it is recommended that the ObjectOutputStream.reset() method be called so that references to previously written objects may be garbage collected.

FileOutputStream fos = new FileOutputStream("data.txt");
ObjectOutputStream oos = new ObjectOutputStream(fos);
oos.writeObject(new Date());
oos.reset();  // Reset the Object-Handle table to its initial state
// ... 

Risk Assessment

Assuming that infinite heap space is available can result in denial of service.

Related Vulnerabilities

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

Other Languages

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The Apache Geronimo bug described by GERONIMO-4224 results in an OutOfMemoryError exception thrown by the WebAccessLogViewer when the access log file size is too large.

Automated Detection

Related Guidelines

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Bibliography

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Related Vulnerabilities

GERONIMO-4224

References

\[[Sun 06|AA. Java References#Sun 06]\] [Garbage Collection Ergonomics|http://java.sun.com/javase/6/docs/technotes/guides/vm/gc-ergonomics.html ], "Default values for the Initial and Maximum heap size"
\[[Java 06|AA. Java References#Java 06]\] [java - the Java application launcher|http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html ], "Syntax for increasing the heap size"
\[[Sun 03|AA. Java References#Sun 03]\] Chapter 5: Tuning the Java Runtime System, [Tuning the Java Heap|http://docs.sun.com/source/817-2180-10/pt_chap5.html#wp57027] 
\[[API 06|AA. Java References#API 06]\] Class ObjectInputStream and ObjectOutputStream
\[[SDN 08|AA. Java References#SDN 08]\] [Serialization FAQ|http://java.sun.com/javase/technologies/core/basic/serializationFAQ.jsp] 
\[[MITRE 09|AA. Java References#MITRE 09]\] [CWE ID 400|http://cwe.mitre.org/data/definitions/400.html] "Uncontrolled Resource Consumption (aka 'Resource Exhaustion')"

MSC06-J. Finish every set of statements associated with a case label with a break statement      49. Miscellaneous (MSC)      MSC08-J. Limit the lifetime of sensitive data