{-# LANGUAGE OverloadedStrings #-} -- | Sanatize HTML to prevent XSS attacks. -- -- See README.md for more details. module Text.HTML.SanitizeXSS ( -- * Sanitize sanitize , sanitizeBalance , sanitizeXSS -- * Custom filtering , filterTags , safeTags , balanceTags -- * Utilities , sanitizeAttribute , sanitaryURI ) where import Text.HTML.SanitizeXSS.Css import Text.HTML.TagSoup import Data.Set (Set(), member, notMember, (\\), fromList, fromAscList) import Data.Char ( toLower ) import Data.Text (Text) import qualified Data.Text as T import Network.URI ( parseURIReference, URI (..), isAllowedInURI, escapeURIString, uriScheme ) import Codec.Binary.UTF8.String ( encodeString ) import Data.Maybe (catMaybes) -- | Sanitize HTML to prevent XSS attacks. This is equivalent to @filterTags safeTags@. sanitize :: Text -> Text sanitize = sanitizeXSS -- | alias of sanitize function sanitizeXSS :: Text -> Text sanitizeXSS = filterTags safeTags -- | 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) -- | Filter which makes sure the tags are balanced. Use with 'filterTags' and 'safeTags' to create a custom filter. balanceTags :: [Tag Text] -> [Tag Text] balanceTags = balance [] -- | Parse the given text to a list of tags, apply the given filtering function, and render back to HTML. -- You can insert your own custom filtering but make sure you compose your filtering function with 'safeTags'! filterTags :: ([Tag Text] -> [Tag Text]) -> Text -> Text filterTags f = renderTagsOptions renderOptions { optMinimize = \x -> x `member` voidElems -- converts to , converts to } . f . canonicalizeTags . parseTags voidElems :: Set T.Text voidElems = fromAscList $ T.words $ T.pack "area base br col command embed hr img input keygen link meta param source track wbr" balance :: [Text] -- ^ unclosed tags -> [Tag Text] -> [Tag Text] balance unclosed [] = map TagClose $ filter (`notMember` voidElems) unclosed balance (x:xs) tags'@(TagClose name:tags) | x == name = TagClose name : balance xs tags | x `member` voidElems = balance xs tags' | otherwise = TagOpen name [] : TagClose name : balance (x:xs) tags balance unclosed (TagOpen name as : tags) = TagOpen name as : balance (name : unclosed) tags balance unclosed (t:ts) = t : balance unclosed ts -- | Filters out any usafe tags and attributes. Use with filterTags to create a custom filter. safeTags :: [Tag Text] -> [Tag Text] safeTags [] = [] safeTags (t@(TagClose name):tags) | safeTagName name = t : safeTags tags | otherwise = safeTags tags safeTags (TagOpen name attributes:tags) | safeTagName name = TagOpen name (catMaybes $ map sanitizeAttribute attributes) : safeTags tags | otherwise = safeTags tags safeTags (t:tags) = t:safeTags 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) -- | low-level API if you have your own HTML parser. Used by safeTags. sanitizeAttribute :: (Text, Text) -> Maybe (Text, Text) sanitizeAttribute ("style", value) = let css = sanitizeCSS value in if T.null css then Nothing else Just ("style", css) sanitizeAttribute attr | safeAttribute attr = Just attr | otherwise = Nothing -- | Returns @True@ if the specified URI is not a potential security risk. sanitaryURI :: Text -> Bool sanitaryURI u = case parseURIReference (escapeURI $ T.unpack u) of Just p -> (null (uriScheme p)) || ((map toLower $ init $ uriScheme p) `member` safeURISchemes) Nothing -> False -- | Escape unicode characters in a URI. Characters that are -- already valid in a URI, including % and ?, are left alone. escapeURI :: String -> String escapeURI = escapeURIString isAllowedInURI . encodeString safeURISchemes :: Set String safeURISchemes = fromList acceptable_protocols sanitaryTags :: Set Text sanitaryTags = fromList (acceptable_elements ++ mathml_elements ++ svg_elements) \\ (fromList svg_allow_local_href) -- extra filtering not implemented 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 allowed_html_uri_attributes :: [Text] allowed_html_uri_attributes = ["href", "src", "cite", "action", "longdesc"] uri_attributes :: Set Text uri_attributes = fromList $ allowed_html_uri_attributes ++ ["xlink:href", "xml:base"] acceptable_elements :: [Text] acceptable_elements = ["a", "abbr", "acronym", "address", "area", "article", "aside", "audio", "b", "big", "blockquote", "br", "button", "canvas", "caption", "center", "cite", "code", "col", "colgroup", "command", "datagrid", "datalist", "dd", "del", "details", "dfn", "dialog", "dir", "div", "dl", "dt", "em", "event-source", "fieldset", "figcaption", "figure", "footer", "font", "form", "header", "h1", "h2", "h3", "h4", "h5", "h6", "hr", "i", "img", "input", "ins", "keygen", "kbd", "label", "legend", "li", "m", "main", "map", "menu", "meter", "multicol", "nav", "nextid", "ol", "output", "optgroup", "option", "p", "pre", "progress", "q", "s", "samp", "section", "select", "small", "sound", "source", "spacer", "span", "strike", "strong", "sub", "sup", "table", "tbody", "td", "textarea", "time", "tfoot", "th", "thead", "tr", "tt", "u", "ul", "var", "video"] mathml_elements :: [Text] mathml_elements = ["maction", "math", "merror", "mfrac", "mi", "mmultiscripts", "mn", "mo", "mover", "mpadded", "mphantom", "mprescripts", "mroot", "mrow", "mspace", "msqrt", "mstyle", "msub", "msubsup", "msup", "mtable", "mtd", "mtext", "mtr", "munder", "munderover", "none"] -- this should include altGlyph I think svg_elements :: [Text] svg_elements = ["a", "animate", "animateColor", "animateMotion", "animateTransform", "clipPath", "circle", "defs", "desc", "ellipse", "font-face", "font-face-name", "font-face-src", "g", "glyph", "hkern", "linearGradient", "line", "marker", "metadata", "missing-glyph", "mpath", "path", "polygon", "polyline", "radialGradient", "rect", "set", "stop", "svg", "switch", "text", "title", "tspan", "use"] acceptable_attributes :: [Text] acceptable_attributes = ["abbr", "accept", "accept-charset", "accesskey", "align", "alt", "autocomplete", "autofocus", "axis", "background", "balance", "bgcolor", "bgproperties", "border", "bordercolor", "bordercolordark", "bordercolorlight", "bottompadding", "cellpadding", "cellspacing", "ch", "challenge", "char", "charoff", "choff", "charset", "checked", "class", "clear", "color", "cols", "colspan", "compact", "contenteditable", "controls", "coords", -- "data", TODO: allow this with further filtering "datafld", "datapagesize", "datasrc", "datetime", "default", "delay", "dir", "disabled", "draggable", "dynsrc", "enctype", "end", "face", "for", "form", "frame", "galleryimg", "gutter", "headers", "height", "hidefocus", "hidden", "high", "hreflang", "hspace", "icon", "id", "inputmode", "ismap", "keytype", "label", "leftspacing", "lang", "list", "loop", "loopcount", "loopend", "loopstart", "low", "lowsrc", "max", "maxlength", "media", "method", "min", "multiple", "name", "nohref", "noshade", "nowrap", "open", "optimum", "pattern", "ping", "point-size", "prompt", "pqg", "radiogroup", "readonly", "rel", "repeat-max", "repeat-min", "replace", "required", "rev", "rightspacing", "rows", "rowspan", "rules", "scope", "selected", "shape", "size", "span", "start", "step", "style", -- gets further filtering "summary", "suppress", "tabindex", "target", "template", "title", "toppadding", "type", "unselectable", "usemap", "urn", "valign", "value", "variable", "volume", "vspace", "vrml", "width", "wrap", "xml:lang"] acceptable_protocols :: [String] acceptable_protocols = [ "ed2k", "ftp", "http", "https", "irc", "mailto", "news", "gopher", "nntp", "telnet", "webcal", "xmpp", "callto", "feed", "urn", "aim", "rsync", "tag", "ssh", "sftp", "rtsp", "afs" ] mathml_attributes :: [Text] mathml_attributes = ["actiontype", "align", "columnalign", "columnalign", "columnalign", "columnlines", "columnspacing", "columnspan", "depth", "display", "displaystyle", "equalcolumns", "equalrows", "fence", "fontstyle", "fontweight", "frame", "height", "linethickness", "lspace", "mathbackground", "mathcolor", "mathvariant", "mathvariant", "maxsize", "minsize", "other", "rowalign", "rowalign", "rowalign", "rowlines", "rowspacing", "rowspan", "rspace", "scriptlevel", "selection", "separator", "stretchy", "width", "width", "xlink:href", "xlink:show", "xlink:type", "xmlns", "xmlns:xlink"] svg_attributes :: [Text] svg_attributes = ["accent-height", "accumulate", "additive", "alphabetic", "arabic-form", "ascent", "attributeName", "attributeType", "baseProfile", "bbox", "begin", "by", "calcMode", "cap-height", "class", "clip-path", "color", "color-rendering", "content", "cx", "cy", "d", "dx", "dy", "descent", "display", "dur", "end", "fill", "fill-opacity", "fill-rule", "font-family", "font-size", "font-stretch", "font-style", "font-variant", "font-weight", "from", "fx", "fy", "g1", "g2", "glyph-name", "gradientUnits", "hanging", "height", "horiz-adv-x", "horiz-origin-x", "id", "ideographic", "k", "keyPoints", "keySplines", "keyTimes", "lang", "marker-end", "marker-mid", "marker-start", "markerHeight", "markerUnits", "markerWidth", "mathematical", "max", "min", "name", "offset", "opacity", "orient", "origin", "overline-position", "overline-thickness", "panose-1", "path", "pathLength", "points", "preserveAspectRatio", "r", "refX", "refY", "repeatCount", "repeatDur", "requiredExtensions", "requiredFeatures", "restart", "rotate", "rx", "ry", "slope", "stemh", "stemv", "stop-color", "stop-opacity", "strikethrough-position", "strikethrough-thickness", "stroke", "stroke-dasharray", "stroke-dashoffset", "stroke-linecap", "stroke-linejoin", "stroke-miterlimit", "stroke-opacity", "stroke-width", "systemLanguage", "target", "text-anchor", "to", "transform", "type", "u1", "u2", "underline-position", "underline-thickness", "unicode", "unicode-range", "units-per-em", "values", "version", "viewBox", "visibility", "width", "widths", "x", "x-height", "x1", "x2", "xlink:actuate", "xlink:arcrole", "xlink:href", "xlink:role", "xlink:show", "xlink:title", "xlink:type", "xml:base", "xml:lang", "xml:space", "xmlns", "xmlns:xlink", "y", "y1", "y2", "zoomAndPan"] -- the values for these need to be escaped svg_attr_val_allows_ref :: [Text] svg_attr_val_allows_ref = ["clip-path", "color-profile", "cursor", "fill", "filter", "marker", "marker-start", "marker-mid", "marker-end", "mask", "stroke"] svg_allow_local_href :: [Text] svg_allow_local_href = ["altGlyph", "animate", "animateColor", "animateMotion", "animateTransform", "cursor", "feImage", "filter", "linearGradient", "pattern", "radialGradient", "textpath", "tref", "set", "use"]