Class DefaultEncoder
- java.lang.Object
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- org.owasp.esapi.reference.DefaultEncoder
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- All Implemented Interfaces:
Encoder
public class DefaultEncoder extends java.lang.Object implements Encoder
Reference implementation of the Encoder interface. This implementation takes a whitelist approach to encoding, meaning that everything not specifically identified in a list of "immune" characters is encoded.- Since:
- June 1, 2007
- Author:
- Jeff Williams (jeff.williams .at. aspectsecurity.com) Aspect Security
- See Also:
Encoder
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Field Summary
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Fields inherited from interface org.owasp.esapi.Encoder
CHAR_ALPHANUMERICS, CHAR_DIGITS, CHAR_LETTERS, CHAR_LOWERS, CHAR_PASSWORD_DIGITS, CHAR_PASSWORD_LETTERS, CHAR_PASSWORD_LOWERS, CHAR_PASSWORD_SPECIALS, CHAR_PASSWORD_UPPERS, CHAR_SPECIALS, CHAR_UPPERS
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Constructor Summary
Constructors Constructor Description DefaultEncoder(java.util.List<java.lang.String> codecNames)
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description java.lang.String
canonicalize(java.lang.String input)
This method is equivalent to callingjava.lang.String
canonicalize(java.lang.String input, boolean strict)
This method is the equivalent to callingjava.lang.String
canonicalize(java.lang.String input, boolean restrictMultiple, boolean restrictMixed)
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 encodingjava.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.static Encoder
getInstance()
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Method Detail
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getInstance
public static Encoder getInstance()
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canonicalize
public java.lang.String canonicalize(java.lang.String input)
This method is equivalent to callingEncoder.canonicalize(input, restrictMultiple, restrictMixed);
The default values for restrictMultiple and restrictMixed come from ESAPI.propertiesEncoder.AllowMultipleEncoding=false Encoder.AllowMixedEncoding=false
- Specified by:
canonicalize
in interfaceEncoder
- Parameters:
input
- the text to canonicalize- Returns:
- a String containing the canonicalized text
- See Also:
canonicalize
, W3C specifications
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canonicalize
public java.lang.String canonicalize(java.lang.String input, boolean strict)
This method is the equivalent to callingEncoder.canonicalize(input, strict, strict);
- Specified by:
canonicalize
in interfaceEncoder
- Parameters:
input
- the text to canonicalizestrict
- true if checking for multiple and mixed encoding is desired, false otherwise- Returns:
- a String containing the canonicalized text
- See Also:
canonicalize
, W3C specifications
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canonicalize
public java.lang.String canonicalize(java.lang.String input, boolean restrictMultiple, boolean restrictMixed)
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. This is configurable in ESAPI.properties using the properties:Encoder.AllowMultipleEncoding=false Encoder.AllowMixedEncoding=false
This method allows you to override the default behavior by directly specifying whether to restrict multiple or mixed encoding. Even if you disable restrictions, 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, false);
- Specified by:
canonicalize
in interfaceEncoder
- Parameters:
input
- the text to canonicalizerestrictMultiple
- true if checking for multiple encoding is desired, false otherwiserestrictMixed
- true if checking for mixed encoding is desired, false otherwise- Returns:
- a String containing the canonicalized text
- See Also:
- W3C specifications
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encodeForHTML
public java.lang.String encodeForHTML(java.lang.String input)
Encode data for use in HTML using HTML entity encodingNote that the following characters: 00-08, 0B-0C, 0E-1F, and 7F-9F
cannot be used in HTML.
- Specified by:
encodeForHTML
in interfaceEncoder
- 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]
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decodeForHTML
public java.lang.String decodeForHTML(java.lang.String input)
Decodes HTML entities.- Specified by:
decodeForHTML
in interfaceEncoder
- Parameters:
input
- theString
to decode- Returns:
- the newly decoded
String
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encodeForHTMLAttribute
public java.lang.String encodeForHTMLAttribute(java.lang.String input)
Encode data for use in HTML attributes.- Specified by:
encodeForHTMLAttribute
in interfaceEncoder
- Parameters:
input
- the text to encode for an HTML attribute- Returns:
- input encoded for use as an HTML attribute
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encodeForCSS
public java.lang.String encodeForCSS(java.lang.String input)
Encode data for use in Cascading Style Sheets (CSS) content.- Specified by:
encodeForCSS
in interfaceEncoder
- Parameters:
input
- the text to encode for CSS- Returns:
- input encoded for CSS
- See Also:
- CSS Syntax [w3.org]
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encodeForJavaScript
public 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:<script> window.setInterval('<%= EVEN IF YOU ENCODE UNTRUSTED DATA YOU ARE XSSED HERE %>'); </script>
- Specified by:
encodeForJavaScript
in interfaceEncoder
- Parameters:
input
- the text to encode for JavaScript- Returns:
- input encoded for use in JavaScript
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encodeForVBScript
public 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- Specified by:
encodeForVBScript
in interfaceEncoder
- Parameters:
input
- the text to encode for VBScript- Returns:
- input encoded for use in VBScript
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encodeForSQL
public 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.- Specified by:
encodeForSQL
in interfaceEncoder
- 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
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encodeForOS
public 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");- Specified by:
encodeForOS
in interfaceEncoder
- 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
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encodeForLDAP
public java.lang.String encodeForLDAP(java.lang.String input)
Encode data for use in LDAP queries.- Specified by:
encodeForLDAP
in interfaceEncoder
- Parameters:
input
- the text to encode for LDAP- Returns:
- input encoded for use in LDAP
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encodeForDN
public java.lang.String encodeForDN(java.lang.String input)
Encode data for use in an LDAP distinguished name.- Specified by:
encodeForDN
in interfaceEncoder
- Parameters:
input
- the text to encode for an LDAP distinguished name- Returns:
- input encoded for use in an LDAP distinguished name
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encodeForXPath
public 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.- Specified by:
encodeForXPath
in interfaceEncoder
- 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]
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encodeForXML
public 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.
- Specified by:
encodeForXML
in interfaceEncoder
- Parameters:
input
- the text to encode for XML- Returns:
- input encoded for use in XML
- See Also:
- XML Encoding Standard
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encodeForXMLAttribute
public 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.
- Specified by:
encodeForXMLAttribute
in interfaceEncoder
- 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
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encodeForURL
public 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.- Specified by:
encodeForURL
in interfaceEncoder
- 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
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decodeFromURL
public 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.- Specified by:
decodeFromURL
in interfaceEncoder
- Parameters:
input
- the text to decode from an encoded URL- Returns:
- the decoded URL value
- Throws:
EncodingException
- if decoding fails
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encodeForBase64
public java.lang.String encodeForBase64(byte[] input, boolean wrap)
Encode for Base64.- Specified by:
encodeForBase64
in interfaceEncoder
- Parameters:
input
- the text to encode for Base64wrap
- the encoder will wrap lines every 64 characters of output- Returns:
- input encoded for Base64
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decodeFromBase64
public byte[] decodeFromBase64(java.lang.String input) throws java.io.IOException
Decode data encoded with BASE-64 encoding.- Specified by:
decodeFromBase64
in interfaceEncoder
- Parameters:
input
- the Base64 text to decode- Returns:
- input decoded from Base64
- Throws:
java.io.IOException
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