Monday, November 19, 2012

How to correctly escape webapp output

1, Escaping must be performed in the last possible place = when writing HTML output

Only when writing a java variable content to the output stream we know if we write the content into a javascript variable, html attribute or as a plain text (html body).

2, Every variable of a String type deserves escaping. Don't escape output only in case you NEED to print HTML.

You may never know how a possibly malicious content got into your variable. It may be persistent
XSS from DB, session attribute, request parameter.

3, Use the right escaping for the right situation. 

See OWASP's XSS_Prevention_Rules_Summary

Side note: Don't mix URL encoding with URL escaping. 

See HTML appendix B.2.1 and B.2.2

URL encoding
Though there can be UTF-8 characters in the URL, URLs should be transmitted in US-ASCII encoding.

Valid URL follows percent encoding of characters, described in Percent encoding of URI characters.

When URL is not encoded, UTF-8 characters are translated into US-ASCII OOTB by browsers. But if you want to be sure (you can't lose here) you can use new In javascript there is a similar function window.encodeURI().

What MUST BE encoded is a URL parameter name and value. It's confusing but to encode the parameter use Javascript has better name: window.encodeURIComponent().

Don't use URL encoding to perform HTML escaping! (Yes, I've seen that :) )

URL escaping
Let's say we already have a valid (correctly encoded) URL which we want to write into HTML.

Then there are 2 important steps:
1, Ampersand character (&), which may be a part of URL, is used to prefix html entity references. When writing a valid HTML we should escape it the same way as any other ampersand you want to write there. Use ampersand entity: &

2, To write safe HTML = to be sure that URL won't escape from HTML attributes or JavaScript variable (it is allowed to contain apostrophe character) it's good to escape the URL as described in  XSS_Prevention_Rules_Summary, not only the query string part.

When we don't have the URL properly encoded we must escape the whole URL - perform the step #2.

Sunday, November 4, 2012

Theme Template For a Specific Portlet

If you want to have your own template for Sign In portlet, you can simply:

  1. Go to your templates directory (theme/docroot/_diffs/templates/)
  2. Copy portlet.vm into portlet.58.vm (58 is a portlet id for Sign In portlet)
  3. Now, Sign In portlet will use portlet.58.vm, other portlets will use default portlet.vm
The same applies for instanceable portlets (e.g. you can have portlet.101_INSTANCE_ABCDE.vm).

You can find the nice piece of logic for loading a portlet template (both VM and FTL) inside com.liferay.taglib.util.ThemeUtil. It's simple:

  • Let's render portlet portlet with Id: 1_WAR_samplejsonportlet_INSTANCE_UgOvIB6Y3Ppb
  1. Portal first tries to find portlet.1_WAR_samplejsonportlet_INSTANCE_UgOvIB6Y3Ppb.vm
  2. Then tries portlet.1_WAR_samplejsonportlet.vm
  3. Finally use portlet.vm