yesodweb / haskell-xss-sanitize Goto Github PK

View Code? Open in Web Editor NEW

This project forked from gregwebs/haskell-xss-sanitize

20.0 20.0 15.0 104 KB

prevent XSS attacks by sanitizing html (this is different then escaping!)

License: Other

Haskell 100.00%

haskell-xss-sanitize's People

Contributors

Stargazers

Watchers

Forkers

sol juhp asayers duairc b-rich rgaiacs hritchie macressler zoominsoftware fraser-dunlop seereason andys8 polimorphic skyfold andreasabel

haskell-xss-sanitize's Issues

0.3.5.7 install failure on ubuntu

garbetsp@biostat1427:~/Projects$ cabal install xss-sanitize
Resolving dependencies...
Downloading xss-sanitize-0.3.5.7...
Failed to install xss-sanitize-0.3.5.7
Build log ( /home/garbetsp/.cabal/logs/xss-sanitize-0.3.5.7.log ):
cabal: /home/garbetsp/.cabal/logs/xss-sanitize-0.3.5.7.log: does not exist

I tried a direct download from git and this fails as well. It creates no log and aborts on install. Tried the earlier 0.3.5.6 release and got the same result.

Function to get rid of invalid html

I am looking into rendering some user-submitted html, so unsurprisingly I'm planning on using this library to sanitize it.

However:

There is no guarantee for how a browser will display invalid HTML, so there is no guarantee that this function will protect your HTML from being broken by a user's html.

This makes me pretty nervous. Preventing invalid HTML from breaking the rest of the page is pretty essential.

How difficult would it be to add a functionality that would get rid of or fix invalid html to avoid this problem? Or at least invalid html that causes problems in practice.

Are there any known examples of html that is problematic even after sanitization? I was hoping that a parent div with some overflow: hidden would be sufficient.

Script and style tag contents should likely be cleared

Currently sanitizing script and style stags preserves the internal content as escaped html:

sanitize "<script>console.log('foo');</script>"
-- "console.log(&#39;foo&#39;);"

sanitize "<style>* { color: red }</style>"
-- "* { color: red }"

This is of course perfectly safe. However it seems very unlikely to be the desired resulting html.

Accordingly it seems like an explicit clear-list of html tags that should be emptied instead of escaped would be useful, with ["script", "style"] as the default list.

One could reasonably argue that <head> should make the list as well.

Bump dep versions in .cabal

In particular, network has hit 2.6+ on hackage and could use a bump.

MathML support need improvements

This was discovery when using Gitit, see jgm/gitit#479.

Summary

Valid MathML tags are sanitezed.

Steps To Reproduce

Generate a simple MathML element with Pandoc.

$ pandoc -f markdown -t html --mathml <<EOF
\$x\$
EOF
<p><math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>x</mi><annotation encoding="application/x-tex">x</annotation></semantics></math></p>

Copy the MathML element and sanitize it.

Actual Results

<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><mi>x</mi>x</math>

This MathML element is invalid.

Expected Results

<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>x</mi><annotation encoding="application/x-tex">x</annotation></semantics></math></p>

This is the unchanged output from Pandoc.

Additional Information

The semantics and annotation tags are valid MathML 3, see http://www.w3.org/TR/MathML/chapter5.html#mixing.semantic.annotations for more information.

Environment Information

$ ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.3
$ ghc-pkg list gitit 
   gitit-0.10.6.1
$ ghc-pkg list pandoc
   pandoc-1.13.3
$ ghc-pkg list texmath
   texmath-0.8.0.1
$ ghc-pkg list xss-sanitize
   xss-sanitize-0.3.5.4

filterTags escapes HTML entities because of TagSoup's defaults

*Text.HTML.SanitizeXSS> filterTags safeTags "text&nbsp;more text"
"text&amp;nbsp;more text"

This would display as "text &nbspmore text" instead of "text more text".

If you add optEscape = id to the renderOptions then TagSoup will stop trying to escape &"<>

*Text.HTML.SanitizeXSS> filterTags safeTags "text&nbsp;more text"
"text&nbsp;more text"

If you are ok with this fix, I'll create a pull request with my changes.

Allow text-2.1 for GHC 9.8

rejecting: text-2.1/installed-4d9a (conflict: xss-sanitize => text>=0.11 && <2.1)

img attribute getting removed

I'm using imgsrc to support high-resolution display images: https://webkit.org/demos/srcset/

<img src="image.jpg" srcset="image-1x.jpg 1x, image-2x.jpg 2x, image-3x.jpg 3x">

Your XSS strips this down to

<img src="image.jpg">

It just gets rid of the srcset. Why, and if srcset isn't really dangerous, can you consider whitelisting it?

Parser improperly handles optional tags under html5 rules

https://html.spec.whatwg.org/multipage/syntax.html#optional-tags

Minimal incorrect example:

-- current
sanitizeBalance "<td>foo<td>bar" == "<td>foo<td>bar</td></td>"

-- correct
sanitizeBalance "<td>foo<td>bar" == "<td>foo</td><td>bar</td>"

-- potentially an option depending on semantics of "balanced"
sanitizeBalance "<td>foo<td>bar" == "<td>foo<td>bar"

If html4 / xhtml5 sanitizing is also desired then separate functions/modules may be needed.

License mismatch between Cabal and LICENSE file

The Cabal file says the library is released under BSD3, but the LICENSE file shipped with the code actually contains a BSD2 license.

use fast-tagsoup

It would be nice to use http://hackage.haskell.org/package/fast-tagsoup

I think this would drop the utf8-string dependency, however it would add text-icu which can be a pain to install.

Support text-2.0

Currently, text-2.0 is excluded by constraint text < 2.

xss-sanitize 0.3.7 causes downstream tests to fail

Here are snippets of what I observed on the stackage build server. I can try to provide better repro instructions upon request.

yesod-markdown-0.12.6.11

    Yesod.Markdown
      converts Markdown to sanitized HTML FAILED [1]
      converts Markdown to unsanitized HTML

    Failures:

      test/Spec.hs:33:9:
      1) Yesod.Markdown converts Markdown to sanitized HTML
           expected: "<h1 id=\"title\">Title</h1><ul><li>one</li><li>two</li><
li>three</li></ul>\n  alert('xxs');\n"
            but got: "<h1 id=\"title\">Title</h1><ul><li>one</li><li>two</li><
li>three</li></ul>"


markdown-0.1.17.4

      test/main.hs:230:26:
      1) html block xss
           expected: "alert(&quot;evil&quot;)"
            but got: ""

Issue with style details still being included

sanitizeBalance sometimes still includes the content within the style tag.

Here's a minimum reproducible example that shows the issue:

λ> sanitizeBalance "<!DOCTYPE><html><style>html{width:100%;max-width:100%}</style></html></DOCTYPE>"
"html{width:100%;max-width:100%}"

This should just return "" and a simple example like this works:

λ> sanitizeBalance "<style>html{width:100%}</style>"

Low-level API only for attributes?

The sanitizeAttribute function is exposed with the following comment:

low-level API if you have your own HTML parser

But safeTagName or sanitaryTags aren't exposed :-(

Export clearTags and explain safeTags is not enough

From the documentation:

You can insert your own custom filtering, but make sure you compose your filtering function with [safeTags] or [safeTagsCustom]

Really this should say:

You can insert your own custom filtering, but make sure you compose your filtering function with (safeTags . clearTags) or (safeTagsCustom . clearTagsCustom)

The problem is, without applying clearTags first, the input may not be sanitized:

Prelude Text.HTML.SanitizeXSS> filterTags safeTags "<iframe></iframe>"
""
Prelude Text.HTML.SanitizeXSS> filterTags safeTags "<script><iframe></iframe>"
"<iframe></iframe>"

This isn't an issue with sanitizeXSS because it composes safeTags with clearTags.

Prelude Text.HTML.SanitizeXSS> sanitizeXSS "<script><iframe></iframe>"
""

I'm happy to make a pull request to fix this.