Xss fix #40136
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Xss fix #40136
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jelbourn
approved these changes
Dec 15, 2020
AndrewKushnir
approved these changes
Dec 15, 2020
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LGTM, thanks for the fix @mhevery 👍
(just left a couple minor comments related to comments, nothing critical)
Escape the content of the strings so that it can be safely inserted into a comment node. The issue is that HTML does not specify any way to escape comment end text inside the comment. `<!-- The way you close a comment is with "-->". -->`. Above the `"-->"` is meant to be text not an end to the comment. This can be created programmatically through DOM APIs. ``` div.innerHTML = div.innerHTML ``` One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.) This function escapes the comment text by looking for the closing char sequence `-->` and replace it with `-_-_>` where the `_` is a zero width space `\u200B`. The result is that if a comment contains `-->` text it will render normally but it will not cause the HTML parser to close the comment.
gkalpak
reviewed
Dec 16, 2020
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| const END_COMMENT = /-->/g; | ||
| const END_COMMENT_ESCAPED = '-\u200B-\u200B>'; |
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OOC, why use two \u200Bs? Wouldn't --\u200B> also work?
alxhub
pushed a commit
that referenced
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Dec 16, 2020
Escape the content of the strings so that it can be safely inserted into a comment node. The issue is that HTML does not specify any way to escape comment end text inside the comment. `<!-- The way you close a comment is with "-->". -->`. Above the `"-->"` is meant to be text not an end to the comment. This can be created programmatically through DOM APIs. ``` div.innerHTML = div.innerHTML ``` One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.) This function escapes the comment text by looking for the closing char sequence `-->` and replace it with `-_-_>` where the `_` is a zero width space `\u200B`. The result is that if a comment contains `-->` text it will render normally but it will not cause the HTML parser to close the comment. PR Close #40136
This was referenced Dec 16, 2020
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Escape the content of the strings so that it can be safely inserted into a comment node.
The issue is that HTML does not specify any way to escape comment end text inside the comment.
<!-- The way you close a comment is with "-->". -->. Above the"-->"is meant to be text not an end to the comment. This can be created programmatically through DOM APIs.One would expect that the above code would be safe to do, but it turns out that because comment text is not escaped, the comment may contain text which will prematurely close the comment opening up the application for XSS attack. (In SSR we programmatically create comment nodes which may contain such text and expect them to be safe.)
This function escapes the comment text by looking for the closing char sequence
-->and replace it with-_-_>where the_is a zero width space\u200B. The result is that if a comment contains-->text it will render normally but it will not cause the HTML parser to close the comment.PR Checklist
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