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A Java OutofMemoryError occurs if infinite when the program attempts to use more heap space than is assumed, making the program crash. This error can be generated due to the following possible reasonsavailable. Among other causes, this error may result from the following:

• A memory leak (see MSC04-J. Do not leak memory)
• An infinite loop
• The program requires more memory than is present by default in the heapLimited amounts of default heap memory available
• Incorrect implementation of common data structures (hash tables, vectors, etc.)

Noncompliant Code Example 1

This example uses an unlimited amount of memory, due to which the program can easily exhaust the heap.

• and so on)
• Unbounded deserialization
• 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 reads lines of text from a file and adds each one to a vector until a line with the word "quit" is encountered:A heap error will be generated if the heap continues to be accessed even if there is no memory left in the heap.

public class ShowHeapErrorReadNames {

  private  Vector<String> names = new Vector<String>();
  private final InputStreamReader  String newName=null;
 input;
  private final BufferedReader reader;

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

  }

  public void addNames() throws IOException {
    	dotry {
    		//adding unknown number of records to a list  String newName;
      while (((newName = reader.readLine()) != null) &&
    		//the user can enter as much data as he wants and exhaust the heap
    		System.out.print(" To quit, enter \"quit\"\nEnter record: "         !(newName.equalsIgnoreCase("quit"))) {
        names.addElement(newName);
        System.out.println("adding " + newName);
      }
    } finally {
      input.close();
    }
  }

  public  	try {static void main(String[] args) throws IOException {
    if (args.length != 1) {
      System.out.println("Arguments: [filename]");
      return;
    		newName = reader.readLine();
          		if(!newName.equalsIgnoreCase("quit")){
          			//names are continued to be added without bothering about the size on the heap
          			names.addElement(newName);
          		}
   			} catch (IOException e) {
   			}}
    ReadNames demo = new ReadNames(args[0]);
    demo.addNames();
  }
}

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) {
   System.out.println(newName);

     return ((sb.length() > 0) ? sb.toString() : null);
      	}
      if (((char) c ==  while (!newName.equalsIgnoreCase("quit")'\n') || ((char) c == '\r')) {
        break;
      }
      sb.append((char) c);
    }
    return sb.toString();
  }

  public static void main(String[] args) {
 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);
        ShowHeapErrorif demo = new ShowHeapError((newName == null || newName.equalsIgnoreCase("quit")) {
          break;
        }
        names.addElement(newName);
        System.out.println("adding " + newName);
      }
   demo.addNames } finally {
      input.close();
    }
  }

Compliant Solution 1

To handle this problem, where the data structure size is so big that the heap gets exhausted, the user should consider using databases, where the record will get written on to the disk. Hence, this structure will never outgrow the heap.

In the above example, the user can reuse a single long variable where the input gets stored and write that value into a simple database containing a table User with a field userID and any other required fields. This will prevent the heap from getting exhausted.

Noncompliant Code Example 2

In this example, the program needs more memory on the heap than the default. In a server-class machine running either VM (client or server) with a parallel garbage collector, the default initial and maximum heap sizes are as follows for J2SE 5.0 \[1\]:

}

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 initial heap size: larger of 1/64th 64 of the machine's physical memory on the machine or some reasonable minimum.
• maximum Maximum heap size: smaller of 1/4th 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/

...

4 of 

...

2GB RAM = 

...

512MB)

...

 * Considering long values being entered (64 bits each, 
 * the max number of elements

...

 would be 

...

512MB/

...

64 bits = 
 * 67108864)

...

 */

...

public class ReadNames {
  // Accepts unknown number of records
  Vector<Long> names = new Vector<Long>(

...

); 
  

...

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

...

 IDs than 

...

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 {
    

...

  input.close();
    

...

}

...

...

}

  

...

public static void main(String[] args) {
    

...

ReadNames demo = new 

...

ReadNames();

...

...

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 MarkupThis exception can be avoided by making sure that there are no infinite loops or memory leaks. If the programmer knows that the application would require a lot of memory, he can increase the heap size in Java using the following runtime parameters \[2\]:

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

For example:,

java -Xms128m -Xmx512m ShowHeapErrorReadNames

Here we have set the initial heap size as 128Mb is set to 128MB and the maximum heap size as 512Mbto 512MB.

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

Risk Assessment

It is difficult identifying a heap exhaustion, since static analysis tools would not be able to pinpoint anything and the heap size could be different for different machines.

In the case of the heap size being increased through the command line, then the assessment would be as follows:

Assuming infinite heap space can result in denial of service.

In the case of the database solution being used, the cost would increase to high due to the coding of a disk-based solution.

Related Vulnerabilities

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

References

[1] Garbage Collection Ergonomics Default values for the Initial and Maximum heap size

[2] Non Standard Options for java: The Java application launcher Syntax for increasing the heap size

Related Vulnerabilities

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

Bibliography

...

Image Added Image Added Image AddedFIO06-J. Validate user input      07. Input Output (FIO)      FIO31-J. Create a copy of mutable inputs