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Using locale-dependent methods on locale-dependent data can produce unexpected results when the locale is unspecified. Programming language identifiers, protocol keys, and HTML tags are often specified in a particular locale, usually Locale.ENGLISH. However, a user can run the Running a program in a different locale , which may cause the program to behave erratically. It may even be possible may result in unexpected program behavior or even allow an attacker to bypass input filters by changing the default locale. For this these reason, any program that inspects data generated by a locale-dependent function must specify the locale used to generate that data.

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% java -Duser.language=tr Example
TİTLE
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Programs that Many programs only use locale-dependent functions only for presenting outputmethods for outputting information, such as dates. In these cases Provided that the locale-dependent data is not inspected by the program, and it may safely rely on the default locale.

Noncompliant Code Example (toUpperCase())

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Many web apps, such as forum or blogging software, must accept input HTML as input and present then display it as output. Displaying untrusted HTML can subject a web app to XSS (cross-site scripting) or HTML injection vulnerabilities. Therefore, it is vital that HTML be sanitized before sending it to a web browser.

One common step in sanitization is identifying tags that may contain malicious content. The <SCRIPT> tag is one such tag; it typically contains Javascript JavaScript code that is executed by a client's browser. Therefore sanitizing HTML involves identifying <SCRIPT> tags and converting them to something harmless, or deleting them altogetherConsequently, HTML input is commonly filtered for <SCRIPT> tags. However, identifying <SCRIPT> tags is not as simple as it appears.

In HTML, tags are case-insensitive, and can therefore be specified using uppercase, lowercase, or any mixture of cases. This noncompliant code example uses the locale-dependent String.toUpperCase() method to convert an HTML tag to upper case, to check it for further processing. The code must ignore <SCRIPT> tags, as they indicate code that is to be discarded. While the English locale would convert "script" to "SCRIPT", the Turkish locale will convert "script" to "SCRİPT", and the check will fail to prune scripts from further processingdetect the <SCRIPT> tag.

Code Block
bgColor #ffcccc lang java
public static void processTag(String tag) { if (tag.toUpperCase().equals("SCRIPT")) { return; } // process tag }

Compliant Solution (Explicit Locale)

This compliant solution explicitly sets the locale to English to avoid unexpected results.

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Specifying Locale.ROOT is a suitable alternative under conditions where an English-specific locale would not be appropriate.

Compliant Solution (Default Locale)

This compliant solution sets the default locale to English before proceeding with performing string operationscomparisons.

public static void processTag(String tag) {
  Locale.setDefault(Locale.ENGLISH);

  if (tag.toUpperCase().equals("SCRIPT")) {
    return;
  }
  // process tag
}

Compliant Solution (String.equalsIgnoreCase())

This compliant solution bypasses locales entirely by performing a case-insensitive match. The String.equalsIgnoreCase() method creates temporary canonical forms of both strings. This may render them unreadable, but it performs proper comparison without making them dependent on the current locale [Schindler].

public static void processTag(String tag) {
  if (tag.equalsIgnoreCase("SCRIPT")) {
    return;
  }
  // process tag
}

Noncompliant Code Example (FileReader)

Java provides classes for handling input and output which can be based on either bytes or characters. The byte I/O families derive from the InputStream and OutputStream interfaces, and are independent of locale or character encoding. However, the character I/O families derive from Reader and Writer, and they must convert byte sequences into strings and back. Thus, they rely on a specified character encoding to do their conversion. This encoding is indicated by the file.encoding system property, which is part of the current locale. Consequently, a file encoded with one encoding, such as UTF-8, must not be read by a character input method using a different encoding, such as UTF-16.

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import java.io.*;

public class PrintMyself {
  private static String inputFile = "PrintMyself.java";
  private static String outputFile = "PrintMyself.txt";

  public static void main(String[] args) throws IOException {
    BufferedReader reader = new BufferedReader(new FileReader(inputFile));
    PrintWriter writer = new PrintWriter(new FileWriter(outputFile));
    int line = 0;
    while (reader.ready()) {
      line++;
      writer.println(line + ": " + reader.readLine());
    }
    reader.close();
    writer.close();
  }
}

Compliant Solution (Charset)

In this compliant solution, both the input and output files are explicitly encoded using UTF8. This program behaves correctly regardless of the default encoding.

  public static void main(String[] args) throws IOException {
    Charset encoding = Charset.forName("UTF8");
    BufferedReader reader = new BufferedReader(new InputStreamReader( new FileInputStream(inputFile), encoding));
    PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(outputFile), encoding));

    int line = 0;

    /* rest of code unchanged */

Noncompliant Code Example (Date)

While the concepts of days and years are universal, the way in which dates are represented varies across cultures, and are therefore specific to locales. This noncompliant code example examines the current date and prints one of two messages, depending on whether or not the month is June.

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The date is 20.06.2014
It's not June.

Compliant Solution (Explicit Locale)

This compliant solution forces the date to be printed in an English format, regardless of the current locale.

String myString = DateFormat.getDateInstance(DateFormat.MEDIUM, Locale.US).format( rightNow.getTime());
/* ...rest of code unchanged...*/

Compliant Solution (Bypass Locale)

This compliant solution checks the date's MONTH attribute without formatting it. While date representations vary by culture, the contents of a Calendar date do not. Consequently, this code works in any locale.

if (rightNow.get(Calendar.MONTH) == Calendar.JUNE) {
/* ...rest of code unchanged...*/

Risk Assessment

Failure to specify the appropriate locale when using locale-dependent methods on local-dependent data without specifying the appropriate locale may result in unexpected behavior.

Android Implementation Details

A developer can specify locale on Android using java.util.Locale.

Bibliography

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