org.owasp.esapi
Interface Encoder

All Known Implementing Classes:

DefaultEncoder

public interface Encoder

The Encoder interface contains a number of methods for decoding input and encoding output so that it will be safe for a variety of interpreters. To prevent double-encoding, callers should make sure input does not already contain encoded characters by calling canonicalize. Validator implementations should call canonicalize on user input before validating to prevent encoded attacks.

All of the methods must use a "whitelist" or "positive" security model. For the encoding methods, this means that all characters should be encoded, except for a specific list of "immune" characters that are known to be safe.

The Encoder performs two key functions, encoding and decoding. These functions rely on a set of codecs that can be found in the org.owasp.esapi.codecs package. These include:

• CSS Escaping
• HTMLEntity Encoding
• JavaScript Escaping
• MySQL Escaping
• Oracle Escaping
• Percent Encoding (aka URL Encoding)
• Unix Escaping
• VBScript Escaping
• Windows Encoding

Since:

June 1, 2007

Author:

Jeff Williams (jeff.williams .at. aspectsecurity.com) Aspect Security

Field Summary

static char[]	CHAR_ALPHANUMERICS Deprecated. Use EncoderConstants.CHAR_ALPHANUMERICS instead
static char[]	CHAR_DIGITS Deprecated. Use EncoderConstants.CHAR_DIGITS instead
static char[]	CHAR_LETTERS Deprecated. Use EncoderConstants.CHAR_LETTERS instead
static char[]	CHAR_LOWERS Deprecated. Use EncoderConstants.CHAR_LOWERS instead
static char[]	CHAR_PASSWORD_DIGITS Deprecated. Use EncoderConstants.CHAR_PASSWORD_DIGITS instead
static char[]	CHAR_PASSWORD_LETTERS Deprecated. Use EncoderConstants.CHAR_PASSWORD_LETTERS instead
static char[]	CHAR_PASSWORD_LOWERS Deprecated. Use EncoderConstants.CHAR_PASSWORD_LOWERS instead
static char[]	CHAR_PASSWORD_SPECIALS Deprecated. Use EncoderConstants.CHAR_PASSWORD_SPECIALS instead
static char[]	CHAR_PASSWORD_UPPERS Deprecated. Use EncoderConstants.CHAR_PASSWORD_UPPERS instead
static char[]	CHAR_SPECIALS Deprecated. Use EncoderConstants.CHAR_SPECIALS instead
static char[]	CHAR_UPPERS Deprecated. Use EncoderConstants.CHAR_UPPERS instead

Method Summary

java.lang.String	canonicalize(java.lang.String input) This method is equivalent to calling
java.lang.String	canonicalize(java.lang.String input, boolean strict) Canonicalization is simply the operation of reducing a possibly encoded string down to its simplest form.
java.lang.String	decodeForHTML(java.lang.String input) Decodes HTML entities.
byte[]	decodeFromBase64(java.lang.String input) Decode data encoded with BASE-64 encoding.
java.lang.String	decodeFromURL(java.lang.String input) Decode from URL.
java.lang.String	encodeForBase64(byte[] input, boolean wrap) Encode for Base64.
java.lang.String	encodeForCSS(java.lang.String input) Encode data for use in Cascading Style Sheets (CSS) content.
java.lang.String	encodeForDN(java.lang.String input) Encode data for use in an LDAP distinguished name.
java.lang.String	encodeForHTML(java.lang.String input) Encode data for use in HTML using HTML entity encoding
java.lang.String	encodeForHTMLAttribute(java.lang.String input) Encode data for use in HTML attributes.
java.lang.String	encodeForJavaScript(java.lang.String input) Encode data for insertion inside a data value or function argument in JavaScript.
java.lang.String	encodeForLDAP(java.lang.String input) Encode data for use in LDAP queries.
java.lang.String	encodeForOS(Codec codec, java.lang.String input) Encode for an operating system command shell according to the selected codec (appropriate codecs include the WindowsCodec and UnixCodec).
java.lang.String	encodeForSQL(Codec codec, java.lang.String input) Encode input for use in a SQL query, according to the selected codec (appropriate codecs include the MySQLCodec and OracleCodec).
java.lang.String	encodeForURL(java.lang.String input) Encode for use in a URL.
java.lang.String	encodeForVBScript(java.lang.String input) Encode data for insertion inside a data value in a Visual Basic script.
java.lang.String	encodeForXML(java.lang.String input) Encode data for use in an XML element.
java.lang.String	encodeForXMLAttribute(java.lang.String input) Encode data for use in an XML attribute.
java.lang.String	encodeForXPath(java.lang.String input) Encode data for use in an XPath query.

Field Detail

CHAR_LOWERS

@Deprecated
static final char[] CHAR_LOWERS

Deprecated. Use EncoderConstants.CHAR_LOWERS instead

CHAR_UPPERS

@Deprecated
static final char[] CHAR_UPPERS

Deprecated. Use EncoderConstants.CHAR_UPPERS instead

CHAR_DIGITS

@Deprecated
static final char[] CHAR_DIGITS

Deprecated. Use EncoderConstants.CHAR_DIGITS instead

CHAR_SPECIALS

@Deprecated
static final char[] CHAR_SPECIALS

Deprecated. Use EncoderConstants.CHAR_SPECIALS instead

CHAR_LETTERS

@Deprecated
static final char[] CHAR_LETTERS

Deprecated. Use EncoderConstants.CHAR_LETTERS instead

CHAR_ALPHANUMERICS

@Deprecated
static final char[] CHAR_ALPHANUMERICS

Deprecated. Use EncoderConstants.CHAR_ALPHANUMERICS instead

CHAR_PASSWORD_LOWERS

@Deprecated
static final char[] CHAR_PASSWORD_LOWERS

Deprecated. Use EncoderConstants.CHAR_PASSWORD_LOWERS instead

Password character set, is alphanumerics (without l, i, I, o, O, and 0) selected specials like + (bad for URL encoding, | is like i and 1, etc...)

CHAR_PASSWORD_UPPERS

@Deprecated
static final char[] CHAR_PASSWORD_UPPERS

Deprecated. Use EncoderConstants.CHAR_PASSWORD_UPPERS instead

CHAR_PASSWORD_DIGITS

@Deprecated
static final char[] CHAR_PASSWORD_DIGITS

Deprecated. Use EncoderConstants.CHAR_PASSWORD_DIGITS instead

CHAR_PASSWORD_SPECIALS

@Deprecated
static final char[] CHAR_PASSWORD_SPECIALS

Deprecated. Use EncoderConstants.CHAR_PASSWORD_SPECIALS instead

CHAR_PASSWORD_LETTERS

@Deprecated
static final char[] CHAR_PASSWORD_LETTERS

Deprecated. Use EncoderConstants.CHAR_PASSWORD_LETTERS instead

Method Detail

canonicalize

java.lang.String canonicalize(java.lang.String input)

This method is equivalent to calling

Encoder.canonicalize(input, true);

Parameters:

input - the text to canonicalize

Returns:

a String containing the canonicalized text

See Also:

W3C specifications

canonicalize

java.lang.String canonicalize(java.lang.String input,
                              boolean strict)

Canonicalization is simply the operation of reducing a possibly encoded string down to its simplest form. This is important, because attackers frequently use encoding to change their input in a way that will bypass validation filters, but still be interpreted properly by the target of the attack. Note that data encoded more than once is not something that a normal user would generate and should be regarded as an attack.

Everyone says you shouldn't do validation without canonicalizing the data first. This is easier said than done. The canonicalize method can be used to simplify just about any input down to its most basic form. Note that canonicalize doesn't handle Unicode issues, it focuses on higher level encoding and escaping schemes. In addition to simple decoding, canonicalize also handles:

• Perverse but legal variants of escaping schemes
• Multiple escaping (%2526 or <)
• Mixed escaping (%26lt;)
• Nested escaping (%%316 or &%6ct;)
• All combinations of multiple, mixed, and nested encoding/escaping (%253c or ┦gt;)

Using canonicalize is simple. The default is just...

 
     String clean = ESAPI.encoder().canonicalize( request.getParameter("input"));
 

You need to decode untrusted data so that it's safe for ANY downstream interpreter or decoder. For example, if your data goes into a Windows command shell, then into a database, and then to a browser, you're going to need to decode for all of those systems. You can build a custom encoder to canonicalize for your application like this...

 
     ArrayList list = new ArrayList();
     list.add( new WindowsCodec() );
     list.add( new MySQLCodec() );
     list.add( new PercentCodec() );
     Encoder encoder = new DefaultEncoder( list );
     String clean = encoder.canonicalize( request.getParameter( "input" ));
 

In ESAPI, the Validator uses the canonicalize method before it does validation. So all you need to do is to validate as normal and you'll be protected against a host of encoded attacks.

     String input = request.getParameter( "name" );
     String name = ESAPI.validator().isValidInput( "test", input, "FirstName", 20, false);
 

However, the default canonicalize() method only decodes HTMLEntity, percent (URL) encoding, and JavaScript encoding. If you'd like to use a custom canonicalizer with your validator, that's pretty easy too.

 
     ... setup custom encoder as above
     Validator validator = new DefaultValidator( encoder );
     String input = request.getParameter( "name" );
     String name = validator.isValidInput( "test", input, "name", 20, false);
 

Although ESAPI is able to canonicalize multiple, mixed, or nested encoding, it's safer to not accept this stuff in the first place. In ESAPI, the default is "strict" mode that throws an IntrusionException if it receives anything not single-encoded with a single scheme. Currently this is not configurable in ESAPI.properties, but it probably should be. Even if you disable "strict" mode, you'll still get warning messages in the log about each multiple encoding and mixed encoding received.

     // disabling strict mode to allow mixed encoding
     String url = ESAPI.encoder().canonicalize( request.getParameter("url"), false);
 

Parameters:

input - the text to canonicalize

strict - true if checking for double encoding is desired, false otherwise

Returns:

a String containing the canonicalized text

See Also:

W3C specifications

encodeForCSS

java.lang.String encodeForCSS(java.lang.String input)

Encode data for use in Cascading Style Sheets (CSS) content.

Parameters:

input - the text to encode for CSS

Returns:

input encoded for CSS

See Also:

CSS Syntax [w3.org]

encodeForHTML

java.lang.String encodeForHTML(java.lang.String input)

Encode data for use in HTML using HTML entity encoding

Note that the following characters: 00-08, 0B-0C, 0E-1F, and 7F-9F

cannot be used in HTML.

Parameters:

input - the text to encode for HTML

Returns:

input encoded for HTML

See Also:

HTML Encodings [wikipedia.org], SGML Specification [w3.org], XML Specification [w3.org]

decodeForHTML

java.lang.String decodeForHTML(java.lang.String input)

Decodes HTML entities.

Parameters:

input - the String to decode

Returns:

the newly decoded String

encodeForHTMLAttribute

java.lang.String encodeForHTMLAttribute(java.lang.String input)

Encode data for use in HTML attributes.

Parameters:

input - the text to encode for an HTML attribute

Returns:

input encoded for use as an HTML attribute

encodeForJavaScript

java.lang.String encodeForJavaScript(java.lang.String input)

Encode data for insertion inside a data value or function argument in JavaScript. Including user data directly inside a script is quite dangerous. Great care must be taken to prevent including user data directly into script code itself, as no amount of encoding will prevent attacks there. Please note there are some JavaScript functions that can never safely receive untrusted data as input – even if the user input is encoded. For example:

Parameters:

input - the text to encode for JavaScript

Returns:

input encoded for use in JavaScript

encodeForVBScript

java.lang.String encodeForVBScript(java.lang.String input)

Encode data for insertion inside a data value in a Visual Basic script. Putting user data directly inside a script is quite dangerous. Great care must be taken to prevent putting user data directly into script code itself, as no amount of encoding will prevent attacks there. This method is not recommended as VBScript is only supported by Internet Explorer

Parameters:

input - the text to encode for VBScript

Returns:

input encoded for use in VBScript

encodeForSQL

java.lang.String encodeForSQL(Codec codec,
                              java.lang.String input)

Encode input for use in a SQL query, according to the selected codec (appropriate codecs include the MySQLCodec and OracleCodec). This method is not recommended. The use of the PreparedStatement interface is the preferred approach. However, if for some reason this is impossible, then this method is provided as a weaker alternative. The best approach is to make sure any single-quotes are double-quoted. Another possible approach is to use the {escape} syntax described in the JDBC specification in section 1.5.6. However, this syntax does not work with all drivers, and requires modification of all queries.

Parameters:

codec - a Codec that declares which database 'input' is being encoded for (ie. MySQL, Oracle, etc.)

input - the text to encode for SQL

Returns:

input encoded for use in SQL

See Also:

JDBC Specification

encodeForOS

java.lang.String encodeForOS(Codec codec,
                             java.lang.String input)

Encode for an operating system command shell according to the selected codec (appropriate codecs include the WindowsCodec and UnixCodec). Please note the following recommendations before choosing to use this method: 1) It is strongly recommended that applications avoid making direct OS system calls if possible as such calls are not portable, and they are potentially unsafe. Please use language provided features if at all possible, rather than native OS calls to implement the desired feature. 2) If an OS call cannot be avoided, then it is recommended that the program to be invoked be invoked directly (e.g., System.exec("nameofcommand" + "parameterstocommand");) as this avoids the use of the command shell. The "parameterstocommand" should of course be validated before passing them to the OS command. 3) If you must use this method, then we recommend validating all user supplied input passed to the command shell as well, in addition to using this method in order to make the command shell invocation safe. An example use of this method would be: System.exec("dir " + ESAPI.encodeForOS(WindowsCodec, "parameter(s)tocommandwithuserinput");

Parameters:

codec - a Codec that declares which operating system 'input' is being encoded for (ie. Windows, Unix, etc.)

input - the text to encode for the command shell

Returns:

input encoded for use in command shell

encodeForLDAP

java.lang.String encodeForLDAP(java.lang.String input)

Encode data for use in LDAP queries.

Parameters:

input - the text to encode for LDAP

Returns:

input encoded for use in LDAP

encodeForDN

java.lang.String encodeForDN(java.lang.String input)

Encode data for use in an LDAP distinguished name.

Parameters:

input - the text to encode for an LDAP distinguished name

Returns:

input encoded for use in an LDAP distinguished name

encodeForXPath

java.lang.String encodeForXPath(java.lang.String input)

Encode data for use in an XPath query. NB: The reference implementation encodes almost everything and may over-encode. The difficulty with XPath encoding is that XPath has no built in mechanism for escaping characters. It is possible to use XQuery in a parameterized way to prevent injection. For more information, refer to this article which specifies the following list of characters as the most dangerous: ^&"*';<>(). This paper suggests disallowing ' and " in queries.

Parameters:

input - the text to encode for XPath

Returns:

input encoded for use in XPath

See Also:

XPath Injection [ibm.com], Blind XPath Injection [packetstormsecurity.org]

encodeForXML

java.lang.String encodeForXML(java.lang.String input)

Encode data for use in an XML element. The implementation should follow the XML Encoding Standard from the W3C.

The use of a real XML parser is strongly encouraged. However, in the hopefully rare case that you need to make sure that data is safe for inclusion in an XML document and cannot use a parse, this method provides a safe mechanism to do so.

Parameters:

input - the text to encode for XML

Returns:

input encoded for use in XML

See Also:

XML Encoding Standard

encodeForXMLAttribute

java.lang.String encodeForXMLAttribute(java.lang.String input)

Encode data for use in an XML attribute. The implementation should follow the XML Encoding Standard from the W3C.

The use of a real XML parser is highly encouraged. However, in the hopefully rare case that you need to make sure that data is safe for inclusion in an XML document and cannot use a parse, this method provides a safe mechanism to do so.

Parameters:

input - the text to encode for use as an XML attribute

Returns:

input encoded for use in an XML attribute

See Also:

XML Encoding Standard

encodeForURL

java.lang.String encodeForURL(java.lang.String input)
                              throws EncodingException

Encode for use in a URL. This method performs URL encoding on the entire string.

Parameters:

input - the text to encode for use in a URL

Returns:

input encoded for use in a URL

Throws:

EncodingException - if encoding fails

See Also:

URL encoding

decodeFromURL

java.lang.String decodeFromURL(java.lang.String input)
                               throws EncodingException

Decode from URL. Implementations should first canonicalize and detect any double-encoding. If this check passes, then the data is decoded using URL decoding.

Parameters:

input - the text to decode from an encoded URL

Returns:

the decoded URL value

Throws:

EncodingException - if decoding fails

encodeForBase64

java.lang.String encodeForBase64(byte[] input,
                                 boolean wrap)

Encode for Base64.

Parameters:

input - the text to encode for Base64

wrap - the encoder will wrap lines every 64 characters of output

Returns:

input encoded for Base64

decodeFromBase64

byte[] decodeFromBase64(java.lang.String input)
                        throws java.io.IOException

Decode data encoded with BASE-64 encoding.

Parameters:

input - the Base64 text to decode

Returns:

input decoded from Base64

Throws:

java.io.IOException