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CDATA Escapes: Difference between revisions
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<dd>CDATA_COMMENT | <dd>CDATA_COMMENT | ||
</dl> | </dl> | ||
===As Image=== | |||
[http://philip.html5.org/misc/cdata.png The transitions as an image.] | |||
===Heuristic Design Notes=== | ===Heuristic Design Notes=== | ||
The heuristic doesn't attempt to detect single or double quotes appearing inside a regular expression literal, because detecting regular expression literals properly is complicated and it's unlikely that </script> would appear in a string literal on the same line with such a regular expression. (I'm assuming the inline minified JS with a minifier that can't escape </script> is a non-issue.) | The heuristic doesn't attempt to detect single or double quotes appearing inside a regular expression literal, because detecting regular expression literals properly is complicated and it's unlikely that </script> would appear in a string literal on the same line with such a regular expression. (I'm assuming the inline minified JS with a minifier that can't escape </script> is a non-issue.) | ||
Revision as of 12:27, 12 August 2009
Requirements
Hard Requirements
- It must be possible to have the string "</script>" in a string literal in inline JavaScript without having to use JS-level escapes. (This possibility may be limited to scripts that use the <!-- ... --> "Hide from old browsers" pattern.)
- It must be possible to have "<!--" and "-->" in string literals in inline JavaScript without having to use JS-level escapes.
- Must not rewind and reparse with different rules.
Medium Requirements
- It should be possible to have the string <!-- in xmp without having the rest of the page eaten up into xmp element.
- It should be possible to have <!-- near the start of a script or style element without having a matching --> and still the trailing part of the page shouldn't get eaten up into the script or style element.
- Pages authored naively for HTML5-parsing-enabled UAs shouldn't be XSS risks in legacy UAs.
- When the author uses comment-like syntax in the fallback markup in iframe, noembed or noframes, the comment-like syntax should span the same character run that it would if it were parsed as markup.
Nice to Have Requirements
- It would be nice for the rest of the page not to get eaten up when the author omits </title> accidentally or mistypes it as <title>.
Proposal
- Remove <!-- ... --> escapes from title, textarea and xmp.
- Make the closing condition for <!-- ... --> in iframe, noembed and noframes match the comment closing conditions exactly.
- Remove <!-- ... --> escapes from script and style and introduce a novel string literal detector heuristic.
String Literal Detector Heuristic
CDATA
<- TAG_OPEN_NON_PCDATA with CDATA as return state
/- CDATA_SLASH
"- CDATA_DOUBLE_QUOTED
'- CDATA_SINGLE_QUOTED
- Anything else
- Stay
CDATA_SLASH
<- TAG_OPEN_NON_PCDATA with CDATA as return state
/- CDATA_LINE_COMMENT
*- CDATA_COMMENT
- Anything else
- CDATA
CDATA_DOUBLE_QUOTED
"- Line feed
- CDATA
\- CDATA_DOUBLE_QUOTED_BACKSLASH
- Anything else
- Stay
CDATA_SINGLE_QUOTED
'- Line feed
- CDATA
\- CDATA_SINGLE_QUOTED_BACKSLASH
- Anything else
- Stay
CDATA_DOUBLE_QUOTED_BACKSLASH
- Line feed
- CDATA
- Anything else
- CDATA_DOUBLE_QUOTED
CDATA_SINGLE_QUOTED_BACKSLASH
- Line feed
- CDATA
- Anything else
- CDATA_SINGLE_QUOTED
CDATA_LINE_COMMENT
- Line feed
- CDATA
<- TAG_OPEN_NON_PCDATA with CDATA_LINE_COMMENT as return state
- Anything else
- Stay
CDATA_COMMENT
*- CDATA_COMMENT_ASTERISK
<- TAG_OPEN_NON_PCDATA with CDATA_COMMENT as return state
- Anything else
- Stay
CDATA_COMMENT_ASTERISK
/- CDATA
<- TAG_OPEN_NON_PCDATA with CDATA_COMMENT as return state
- Anything else
- CDATA_COMMENT
As Image
Heuristic Design Notes
The heuristic doesn't attempt to detect single or double quotes appearing inside a regular expression literal, because detecting regular expression literals properly is complicated and it's unlikely that </script> would appear in a string literal on the same line with such a regular expression. (I'm assuming the inline minified JS with a minifier that can't escape </script> is a non-issue.)