Page History

A Java OutofMemoryError occurs if when the program attempts to use more heap space than what is available. Among other causes, this error may result from the following:

• A memory leak (see MSC04-J. Do not leak memory)
• An
• a memory leak
• an infinite loop
• limited Limited amounts of default heap memory available
• incorrect Incorrect implementation of common data structures (hash tables, vectors, and so on)
• unbound Unbounded deserialization
• writing Writing a large number of objects to an ObjectOutputStream (see SER10-J. Avoid memory and resource leaks during serialization)
• Creating 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 available heap space. 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 {
    Stringtry newName;{
    do {  String   newName;
      // Adding unknown number of records to a list; user can exhaust the heap
while (((newName = reader.readLine()) != null) &&
             !(newName = reader.readLineequalsIgnoreCase("quit")));  {
  
      names.addElement(newName);
      
    } while(newName.equalsIgnoreCase("quit") == false); // Enter "quit" to quit the program
    // Close "reader" and "input"System.out.println("adding " + newName);
      }
    } finally {
      input.close();
    }
  }

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

Wiki MarkupAccording to the Java API \[[API 2006|AA. Bibliography#API 06]\], {{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 documentation

...

\[{{readLine()}}\] 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 abuse a resource exhaustion attack because the user can enter a string of any length. This does not require the noncompliant code example to read input using a loop.

Compliant Solution (Use Databases)

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 being exhausted.

Noncompliant Code Example

In a server-class machine using a parallel garbage collector, the default initial and maximum heap sizes are as follows for J2SE 6.0 \[[Sun 2006|AA. Bibliography#Sun 06]\]:

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.
• 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

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 IDs than the heap can support and thus,
 
       // 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:

  // ...
  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 ensuring that 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 \[[Java 2006|AA. Bibliography#Java 06]\]:

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 \[[API 2006|AA. Bibliography#API 06]\], Class {{ObjectInputStream}} documentation

...

.

By design, objects are written to the stream only on their first appearance therein. For subsequent appearances, the stream writes a handle to the earlier appearance of the object. The ObjectOutputStream maintains a table that maps previously-written objects to their corresponding handles. This table remains live until the stream is closed; consequently, it prevents garbage collection of previously-written objects. 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

Make judicious use of the ObjectOutputStream.reset() method to clear references to previously written objects and consequently permit them to be garbage collected. Note that this will cause subsequent writes of a previously-written object to be treated as though they were the initial write, leading to multiple copies of the object in the serialized data stream. This issue must be addressed to enable correct program operation.

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

...

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 Added

Related Vulnerabilities

GERONIMO-4224

Bibliography

\[[Sun 2006|AA. Bibliography#Sun 06]\] [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"
\[[Java 2006|AA. Bibliography#Java 06]\] [java - the Java application launcher|http://java.sun.com/javase/6/docs/technotes/tools/windows/java.html ], "Syntax for increasing the heap size"
\[[Sun 2003|AA. Bibliography#Sun 03]\] Chapter 5: Tuning the Java Runtime System, [Tuning the Java Heap|http://docs.sun.com/source/817-2180-10/pt_chap5.html#wp57027] 
\[[API 2006|AA. Bibliography#API 06]\] Class ObjectInputStream and ObjectOutputStream
\[[SDN 2008|AA. Bibliography#SDN 08]\] [Serialization FAQ|http://java.sun.com/javase/technologies/core/basic/serializationFAQ.jsp] 
\[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE-400|http://cwe.mitre.org/data/definitions/400.html] "Uncontrolled Resource Consumption ('Resource Exhaustion')," [CWE-770|http://cwe.mitre.org/data/definitions/770.html], "Allocation of Resources Without Limits or Throttling"

MSC10-J. Limit the lifetime of sensitive data      49. Miscellaneous (MSC)      MSC12-J. Prefer using Iterators over Enumerations