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Add support for tag clearing #22

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merged 3 commits into from Sep 18, 2021
Merged

Add support for tag clearing #22

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fb435ff
Add support for tag clearing
tysonzero Sep 17, 2021
abc3dca
Remove unused import
tysonzero Sep 17, 2021
028b4ce
Bump version and add ChangeLog entry
tysonzero Sep 17, 2021
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31 changes: 28 additions & 3 deletions src/Text/HTML/SanitizeXSS.hs
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Expand Up @@ -43,12 +43,12 @@ sanitize = sanitizeXSS

-- | alias of sanitize function
sanitizeXSS :: Text -> Text
sanitizeXSS = filterTags safeTags
sanitizeXSS = filterTags (safeTags . clearTags)

-- | Sanitize HTML to prevent XSS attacks and also make sure the tags are balanced.
-- This is equivalent to @filterTags (balanceTags . safeTags)@.
sanitizeBalance :: Text -> Text
sanitizeBalance = filterTags (balanceTags . safeTags)
sanitizeBalance = filterTags (balanceTags . safeTags . clearTags)

-- | Filter which makes sure the tags are balanced. Use with 'filterTags' and 'safeTags' to create a custom filter.
balanceTags :: [Tag Text] -> [Tag Text]
Expand Down Expand Up @@ -108,13 +108,36 @@ safeTagsCustom safeName sanitizeAttr (TagOpen name attributes:tags)
| otherwise = safeTagsCustom safeName sanitizeAttr tags
safeTagsCustom n a (t:tags) = t : safeTagsCustom n a tags

clearTags :: [Tag Text] -> [Tag Text]
clearTags = clearTagsCustom clearableTagName

clearTagsCustom :: (Text -> Bool) -> [Tag Text] -> [Tag Text]
clearTagsCustom _ [] = []
clearTagsCustom clearableName (tag@(TagOpen name _) : tags)
| clearableName name = tag : go 0 tags
| otherwise = tag : clearTagsCustom clearableName tags
where
go d (t@(TagOpen n _) : ts)
| n /= name = go d ts
| otherwise = go (d + 1) ts
go d (t@(TagClose n) : ts)
| n /= name = go d ts
| d == 0 = t : clearTagsCustom clearableName ts
| otherwise = go (d - 1) ts
go d (t : ts) = go d ts
go d [] = []
clearTagsCustom clearableName (t : tags) = t : clearTagsCustom clearableName tags

safeTagName :: Text -> Bool
safeTagName tagname = tagname `member` sanitaryTags

safeAttribute :: (Text, Text) -> Bool
safeAttribute (name, value) = name `member` sanitaryAttributes &&
(name `notMember` uri_attributes || sanitaryURI value)

clearableTagName :: Text -> Bool
clearableTagName tagname = tagname `member` clearableTags

-- | low-level API if you have your own HTML parser. Used by safeTags.
sanitizeAttribute :: (Text, Text) -> Maybe (Text, Text)
sanitizeAttribute ("style", value) =
Expand Down Expand Up @@ -149,6 +172,9 @@ sanitaryAttributes :: Set Text
sanitaryAttributes = fromList (allowed_html_uri_attributes ++ acceptable_attributes ++ mathml_attributes ++ svg_attributes)
\\ (fromList svg_attr_val_allows_ref) -- extra unescaping not implemented

clearableTags :: Set Text
clearableTags = fromList ["script", "style"]

allowed_html_uri_attributes :: [Text]
allowed_html_uri_attributes = ["href", "src", "cite", "action", "longdesc"]

Expand Down Expand Up @@ -272,4 +298,3 @@ svg_allow_local_href = ["altGlyph", "animate", "animateColor",
"animateMotion", "animateTransform", "cursor", "feImage", "filter",
"linearGradient", "pattern", "radialGradient", "textpath", "tref",
"set", "use"]