[OWASP-ESAPI] Canonicalize now passes all test cases!

Nishi Kumar nishi787 at hotmail.com
Wed Nov 26 23:51:05 EST 2008


Hi Jeff,
 
I have done quite a bit of performance fixes in our applications using JProfiler. I can help.Nishi Kumar
 



From: jeff.williams at owasp.orgTo: owasp-esapi at lists.owasp.orgDate: Wed, 26 Nov 2008 20:52:23 -0500Subject: [OWASP-ESAPI] Canonicalize now passes all test cases!



Hi,
 
The canonicalization engine in ESAPI now passes all the test cases!  You’ll need to sync to SVN to get the code until we can get a jar file built and released. While it was a lot of work to get to this point, the implementation of both the canonicalize() method and all the codecs is very straightforward.
 
Everyone says you shouldn’t do validation without canonicalizing the data first. I said it for many years.  Well, it’s easier said than done. I don’t know of any other library that actually attempts this – please let me know if you do so we can compare results.
 
ESAPI.encoder().canonicalize() now handles:
-        All major application layer encoding/escaping schemes
o   CSS Escaping
o   HTMLEntity Encoding
o   JavaScript Escaping
o   MySQL Escaping
o   Oracle Escaping
o   Percent Encoding (aka URL Encoding)
o   Unix Escaping
o   VBScript Escaping
o   Windows Encoding
-        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 &#x2526gt;)
-        (NOTE: Canonicalize does not currently handle Unicode encoding issues)
 
ESAPI’s canonicalizer couldn’t be simpler to use – the default is just…
 
    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 );
    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.
 
    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 );
    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
    ESAPI.encoder().canonicalize( request.getParameter(“url”), false);
 
If anyone is building a validation engine, you might want to look at the Encoder test cases. There are many examples of multiple, mixed, and nested encoding.
 
http://code.google.com/p/owasp-esapi-java/source/browse/trunk/test/org/owasp/esapi/reference/EncoderTest.java
 
There is still some performance work to do here for anyone who’d like to pitch in.  I’d really like to get a decent performance testing setup in place.
 
--Jeff
 
 
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