// Copyright (c) 2014, David Kitchen <david@buro9.com> // // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are met: // // * Redistributions of source code must retain the above copyright notice, this // list of conditions and the following disclaimer. // // * Redistributions in binary form must reproduce the above copyright notice, // this list of conditions and the following disclaimer in the documentation // and/or other materials provided with the distribution. // // * Neither the name of the organisation (Microcosm) nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" // AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE // IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE // DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE // FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL // DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR // SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, // OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. package bluemonday import ( "encoding/base64" "net/url" "regexp" ) // A selection of regular expressions that can be used as .Matching() rules on // HTML attributes. var ( // CellAlign handles the `align` attribute // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-align CellAlign = regexp.MustCompile(`(?i)^(center|justify|left|right|char)$`) // CellVerticalAlign handles the `valign` attribute // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-valign CellVerticalAlign = regexp.MustCompile(`(?i)^(baseline|bottom|middle|top)$`) // Direction handles the `dir` attribute // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/bdo#attr-dir Direction = regexp.MustCompile(`(?i)^(rtl|ltr)$`) // ImageAlign handles the `align` attribute on the `image` tag // http://www.w3.org/MarkUp/Test/Img/imgtest.html ImageAlign = regexp.MustCompile( `(?i)^(left|right|top|texttop|middle|absmiddle|baseline|bottom|absbottom)$`, ) // Integer describes whole positive integers (including 0) used in places // like td.colspan // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/td#attr-colspan Integer = regexp.MustCompile(`^[0-9]+$`) // ISO8601 according to the W3 group is only a subset of the ISO8601 // standard: http://www.w3.org/TR/NOTE-datetime // // Used in places like time.datetime // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/time#attr-datetime // // Matches patterns: // Year: // YYYY (eg 1997) // Year and month: // YYYY-MM (eg 1997-07) // Complete date: // YYYY-MM-DD (eg 1997-07-16) // Complete date plus hours and minutes: // YYYY-MM-DDThh:mmTZD (eg 1997-07-16T19:20+01:00) // Complete date plus hours, minutes and seconds: // YYYY-MM-DDThh:mm:ssTZD (eg 1997-07-16T19:20:30+01:00) // Complete date plus hours, minutes, seconds and a decimal fraction of a // second // YYYY-MM-DDThh:mm:ss.sTZD (eg 1997-07-16T19:20:30.45+01:00) ISO8601 = regexp.MustCompile( `^[0-9]{4}(-[0-9]{2}(-[0-9]{2}([ T][0-9]{2}(:[0-9]{2}){1,2}(.[0-9]{1,6})` + `?Z?([\+-][0-9]{2}:[0-9]{2})?)?)?)?$`, ) // ListType encapsulates the common value as well as the latest spec // values for lists // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/ol#attr-type ListType = regexp.MustCompile(`(?i)^(circle|disc|square|a|A|i|I|1)$`) // SpaceSeparatedTokens is used in places like `a.rel` and the common attribute // `class` which both contain space delimited lists of data tokens // http://www.w3.org/TR/html-markup/datatypes.html#common.data.tokens-def // Regexp: \p{L} matches unicode letters, \p{N} matches unicode numbers SpaceSeparatedTokens = regexp.MustCompile(`^([\s\p{L}\p{N}_-]+)$`) // Number is a double value used on HTML5 meter and progress elements // http://www.whatwg.org/specs/web-apps/current-work/multipage/the-button-element.html#the-meter-element Number = regexp.MustCompile(`^[-+]?[0-9]*\.?[0-9]+([eE][-+]?[0-9]+)?$`) // NumberOrPercent is used predominantly as units of measurement in width // and height attributes // https://developer.mozilla.org/en-US/docs/Web/HTML/Element/img#attr-height NumberOrPercent = regexp.MustCompile(`^[0-9]+[%]?$`) // Paragraph of text in an attribute such as *.'title', img.alt, etc // https://developer.mozilla.org/en-US/docs/Web/HTML/Global_attributes#attr-title // Note that we are not allowing chars that could close tags like '>' Paragraph = regexp.MustCompile(`^[\p{L}\p{N}\s\-_',\[\]!\./\\\(\)]*$`) // dataURIImagePrefix is used by AllowDataURIImages to define the acceptable // prefix of data URIs that contain common web image formats. // // This is not exported as it's not useful by itself, and only has value // within the AllowDataURIImages func dataURIImagePrefix = regexp.MustCompile( `^image/(gif|jpeg|png|webp);base64,`, ) ) // AllowStandardURLs is a convenience function that will enable rel="nofollow" // on "a", "area" and "link" (if you have allowed those elements) and will // ensure that the URL values are parseable and either relative or belong to the // "mailto", "http", or "https" schemes func (p *Policy) AllowStandardURLs() { // URLs must be parseable by net/url.Parse() p.RequireParseableURLs(true) // !url.IsAbs() is permitted p.AllowRelativeURLs(true) // Most common URL schemes only p.AllowURLSchemes("mailto", "http", "https") // For linking elements we will add rel="nofollow" if it does not already exist // This applies to "a" "area" "link" p.RequireNoFollowOnLinks(true) } // AllowStandardAttributes will enable "id", "title" and the language specific // attributes "dir" and "lang" on all elements that are allowed func (p *Policy) AllowStandardAttributes() { // "dir" "lang" are permitted as both language attributes affect charsets // and direction of text. p.AllowAttrs("dir").Matching(Direction).Globally() p.AllowAttrs( "lang", ).Matching(regexp.MustCompile(`[a-zA-Z]{2,20}`)).Globally() // "id" is permitted. This is pretty much as some HTML elements require this // to work well ("dfn" is an example of a "id" being value) // This does create a risk that JavaScript and CSS within your web page // might identify the wrong elements. Ensure that you select things // accurately p.AllowAttrs("id").Matching( regexp.MustCompile(`[a-zA-Z0-9\:\-_\.]+`), ).Globally() // "title" is permitted as it improves accessibility. p.AllowAttrs("title").Matching(Paragraph).Globally() } // AllowStyling presently enables the class attribute globally. // // Note: When bluemonday ships a CSS parser and we can safely sanitise that, // this will also allow sanitized styling of elements via the style attribute. func (p *Policy) AllowStyling() { // "class" is permitted globally p.AllowAttrs("class").Matching(SpaceSeparatedTokens).Globally() } // AllowImages enables the img element and some popular attributes. It will also // ensure that URL values are parseable. This helper does not enable data URI // images, for that you should also use the AllowDataURIImages() helper. func (p *Policy) AllowImages() { // "img" is permitted p.AllowAttrs("align").Matching(ImageAlign).OnElements("img") p.AllowAttrs("alt").Matching(Paragraph).OnElements("img") p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("img") // Standard URLs enabled p.AllowStandardURLs() p.AllowAttrs("src").OnElements("img") } // AllowDataURIImages permits the use of inline images defined in RFC2397 // http://tools.ietf.org/html/rfc2397 // http://en.wikipedia.org/wiki/Data_URI_scheme // // Images must have a mimetype matching: // image/gif // image/jpeg // image/png // image/webp // // NOTE: There is a potential security risk to allowing data URIs and you should // only permit them on content you already trust. // http://palizine.plynt.com/issues/2010Oct/bypass-xss-filters/ // https://capec.mitre.org/data/definitions/244.html func (p *Policy) AllowDataURIImages() { // URLs must be parseable by net/url.Parse() p.RequireParseableURLs(true) // Supply a function to validate images contained within data URI p.AllowURLSchemeWithCustomPolicy( "data", func(url *url.URL) (allowUrl bool) { if url.RawQuery != "" || url.Fragment != "" { return false } matched := dataURIImagePrefix.FindString(url.Opaque) if matched == "" { return false } _, err := base64.StdEncoding.DecodeString(url.Opaque[len(matched):]) if err != nil { return false } return true }, ) } // AllowLists will enabled ordered and unordered lists, as well as definition // lists func (p *Policy) AllowLists() { // "ol" "ul" are permitted p.AllowAttrs("type").Matching(ListType).OnElements("ol", "ul") // "li" is permitted p.AllowAttrs("type").Matching(ListType).OnElements("li") p.AllowAttrs("value").Matching(Integer).OnElements("li") // "dl" "dt" "dd" are permitted p.AllowElements("dl", "dt", "dd") } // AllowTables will enable a rich set of elements and attributes to describe // HTML tables func (p *Policy) AllowTables() { // "table" is permitted p.AllowAttrs("height", "width").Matching(NumberOrPercent).OnElements("table") p.AllowAttrs("summary").Matching(Paragraph).OnElements("table") // "caption" is permitted p.AllowElements("caption") // "col" "colgroup" are permitted p.AllowAttrs("align").Matching(CellAlign).OnElements("col", "colgroup") p.AllowAttrs("height", "width").Matching( NumberOrPercent, ).OnElements("col", "colgroup") p.AllowAttrs("span").Matching(Integer).OnElements("colgroup", "col") p.AllowAttrs("valign").Matching( CellVerticalAlign, ).OnElements("col", "colgroup") // "thead" "tr" are permitted p.AllowAttrs("align").Matching(CellAlign).OnElements("thead", "tr") p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("thead", "tr") // "td" "th" are permitted p.AllowAttrs("abbr").Matching(Paragraph).OnElements("td", "th") p.AllowAttrs("align").Matching(CellAlign).OnElements("td", "th") p.AllowAttrs("colspan", "rowspan").Matching(Integer).OnElements("td", "th") p.AllowAttrs("headers").Matching( SpaceSeparatedTokens, ).OnElements("td", "th") p.AllowAttrs("height", "width").Matching( NumberOrPercent, ).OnElements("td", "th") p.AllowAttrs( "scope", ).Matching( regexp.MustCompile(`(?i)(?:row|col)(?:group)?`), ).OnElements("td", "th") p.AllowAttrs("valign").Matching(CellVerticalAlign).OnElements("td", "th") p.AllowAttrs("nowrap").Matching( regexp.MustCompile(`(?i)|nowrap`), ).OnElements("td", "th") // "tbody" "tfoot" p.AllowAttrs("align").Matching(CellAlign).OnElements("tbody", "tfoot") p.AllowAttrs("valign").Matching( CellVerticalAlign, ).OnElements("tbody", "tfoot") }