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https://issues.apache.org/jira/browse/LANG-1042?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14163426#comment-14163426
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Duncan Jones commented on LANG-1042:
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It's not really clear from the Javadocs what these methods are supposed to
achieve. Clearly you were expecting the methods to render safe any user input
that might be directly injected into other pieces of HTML. Looking at the code,
it seems they only replace named entities (for XML this includes escaping {{'}}
to {{'}}). At the very least, we should improve the Javadocs to make
it clearer what is being escaped.
If our goal is to sanitise user input, then we should consider whether escaping
single quotes is the only change to make. Any such change would break
compatibility with earlier versions, so I'm not sure we could address this
before 4.0 (unless we are convinced it's a bug, which is hard to prove since
the docs are so vague).
> StringEscapeUtils.escapeHtml() does not escape single quote
> -----------------------------------------------------------
>
> Key: LANG-1042
> URL: https://issues.apache.org/jira/browse/LANG-1042
> Project: Commons Lang
> Issue Type: Bug
> Reporter: Robert Sussland
> Priority: Critical
>
> The String Escape Utils should ensure that encoded data cannot escape from a
> string. However in HTML (starting with 1.0 and until the present), attribute
> values may be denoted by either single or double quotes. Therefore single
> quotes need to be escaped just as much as double quotes.
> From the standard: http://www.w3.org/TR/html4/intro/sgmltut.html#h-3.2.2
> {quote}
> By default, SGML requires that all attribute values be delimited using either
> double quotation marks (ASCII decimal 34) or single quotation marks (ASCII
> decimal 39). Single quote marks can be included within the attribute value
> when the value is delimited by double quote marks, and vice versa. Authors
> may also use numeric character references to represent double quotes
> (&#34\;) and single quotes (&#39\;). For double quotes authors can
> also use the character entity reference ".
> {quote}
> Note that there have been several bugs in the wild in which string encoders
> use this library under the hood, and as a result fail to properly escape html
> attributes in which user input is stored:
> <div title='<%=user_data%>'>Howdy</div>
> if user_data = ' onclick='payload' '
> then an attacker can inject their code into the page even if the developer is
> using the string escape utils to escape the user string.
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