| // 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 all anchors 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 whitelisted |
| 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") |
| } |
