Issue #6861 has been reported by spastorino (Santiago Pastorino).

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Bug #6861: ERB::Util.escape_html is not escaping single quotes
https://bugs.ruby-lang.org/issues/6861

Author: spastorino (Santiago Pastorino)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: 2.0.0dev


We just fixed this issue in Rails
https://groups.google.com/forum/#!msg/rubyonrails-security/kKGNeMrnmiY/r2yM7xy-G48J%5B1-25%5D

Ruby's ERB is not escaping single quotes and this could lead to
security issues like ...

<a href='<%= h link %>' >My Link!</a>
being link = " '; alert(hax) "

OWASP suggest escaping &, <, >, ", ' and /
https://www.owasp.org/index.php/XSS_%28Cross_Site_Scripting%29_Prevention_Cheat_Sheet#RULE_.231_-_HTML_Escape_Before_Inserting_Untrusted_Data_into_HTML_Element_Content

About / I don't think could lead to issues but that's another story.

You have the right code in CGI.escapeHTML
https://github.com/ruby/ruby/blob/c47cca2f/lib/cgi/util.rb#L36 so my
suggestion is to reuse CGI.escapeHTML from ERB::Util

I've sent a pull request https://github.com/ruby/ruby/pull/156


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