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Sanitization rules

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This page was initially seeded with the sanitization lists and rules implemented by the html5lib sanitizer, which in turn was based on Jacques Distler's branch of Instiki, which in turn was based on the sanitization logic in the Universal Feed Parser.

It is hoped that others will add, update, and extend this list based on their experiences in their own products, and furthermore that some will update their products based on these lists. One such product is HTMLPurifier (diffs). Another product is bloglines.

As a suggestion but not as a requirement: people who do update their products to reflect information from this list are encouraged to add a link to this page as a comment in the hopes that it will encourage subsequent maintainers to keep this page up to date.

As a convenience, this script (source) converts these lists into a syntax shared by a number of common programming languages.

Acceptable Elements

  • a
  • abbr
  • acronym
  • address
  • area
  • b
  • bdo
  • big
  • blockquote
  • br
  • button
  • caption
  • center
  • cite
  • code
  • col
  • colgroup
  • dd
  • del
  • dfn
  • dir
  • div
  • dl
  • dt
  • em
  • fieldset
  • font
  • form
  • h1
  • h2
  • h3
  • h4
  • h5
  • h6
  • hr
  • i
  • img
  • input
  • ins
  • kbd
  • label
  • legend
  • li
  • map
  • menu
  • ol
  • optgroup
  • option
  • p
  • pre
  • q
  • s
  • samp
  • select
  • small
  • span
  • strike
  • strong
  • sub
  • sup
  • table
  • tbody
  • td
  • textarea
  • tfoot
  • th
  • thead
  • tr
  • tt
  • u
  • ul
  • var
  • wbr

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

svg Elements

  • a
  • animate
  • animateColor
  • animateMotion
  • animateTransform
  • circle
  • defs
  • desc
  • ellipse
  • font-face
  • font-face-name
  • font-face-src
  • g
  • glyph
  • hkern
  • image
  • linearGradient
  • line
  • marker
  • metadata
  • missing-glyph
  • mpath
  • path
  • polygon
  • polyline
  • radialGradient
  • rect
  • set
  • stop
  • svg
  • switch
  • text
  • title
  • tspan
  • use

Acceptable Attributes

  • abbr
  • accept
  • accept-charset
  • accesskey
  • action
  • align
  • alt
  • axis
  • border
  • cellpadding
  • cellspacing
  • char
  • charoff
  • charset
  • checked
  • cite
  • class
  • clear
  • cols
  • colspan
  • color
  • compact
  • coords
  • datetime
  • dir
  • disabled
  • enctype
  • for
  • frame
  • headers
  • height
  • href
  • hreflang
  • hspace
  • id
  • ismap
  • label
  • lang
  • longdesc
  • maxlength
  • media
  • method
  • multiple
  • name
  • nohref
  • noshade
  • nowrap
  • prompt
  • readonly
  • rel
  • rev
  • rows
  • rowspan
  • rules
  • scope
  • selected
  • shape
  • size
  • span
  • src
  • start
  • style
  • summary
  • tabindex
  • target
  • title
  • type
  • usemap
  • valign
  • value
  • vspace
  • width
  • xml:lang

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

  • accent-height
  • accumulate
  • additive
  • alphabetic
  • arabic-form
  • ascent
  • attributeName
  • attributeType
  • baseProfile
  • bbox
  • begin
  • by
  • calcMode
  • cap-height
  • class
  • color
  • color-rendering
  • content
  • cx
  • cy
  • d
  • dx
  • dy
  • descent
  • display
  • dur
  • end
  • fill
  • 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

CSS Rules

First urls matching the following regular expression are removed:

url\s*\(\s*[^\s)]+?\s*\)\s*

The style strings that don't match the following are deemed obfuscated, and ignored entirely:

^([:,;#%.\sa-zA-Z0-9!]|\w-\w|'[\s\w]+'|"[\s\w]+"|\([\d,\s]+\))*$
^(\s*[-\w]+\s*:\s*[^:;]*(;|$))*$

style Properties

  • azimuth
  • background, background-*
  • border, border-*
  • clear
  • color
  • cursor
  • direction
  • display
  • elevation
  • float
  • font
  • font-family
  • font-size
  • font-style
  • font-variant
  • font-weight
  • height
  • letter-spacing
  • line-height
  • margin, margin-*
  • overflow
  • padding, padding-*
  • pause
  • pause-after
  • pause-before
  • pitch
  • pitch-range
  • richness
  • speak
  • speak-header
  • speak-numeral
  • speak-punctuation
  • speech-rate
  • stress
  • text-align
  • text-decoration
  • text-indent
  • unicode-bidi
  • vertical-align
  • voice-family
  • volume
  • white-space
  • width

style Property Values

  • auto
  • aqua
  • black
  • block
  • blue
  • bold
  • both
  • bottom
  • brown
  • center
  • collapse
  • dashed
  • dotted
  • fuchsia
  • gray
  • green
  • !important
  • italic
  • left
  • lime
  • maroon
  • medium
  • none
  • navy
  • normal
  • nowrap
  • olive
  • pointer
  • purple
  • red
  • right
  • solid
  • silver
  • teal
  • top
  • transparent
  • underline
  • white
  • yellow

In addition, values that match the following regular expression are valid:

^(#[0-9a-f]+|rgb\(\d+%?,\d*%?,?\d*%?\)?|\d{0,2}\.?\d{0,2}(cm|em|ex|in|mm|pc|pt|px|%|,|\))?)$

svg style Properties

  • fill
  • fill-opacity
  • fill-rule
  • stroke
  • stroke-width
  • stroke-linecap
  • stroke-linejoin
  • stroke-opacity

URIs

Attributes whose value is a URI

  • href
  • src
  • cite
  • action
  • longdesc
  • xlink:href
  • xml:base

URI schemes

  • afs
  • aim
  • callto
  • data (see #Safe data URL content types)
  • ed2k
  • feed
  • ftp
  • gopher
  • http
  • https
  • irc
  • mailto
  • news
  • nntp
  • rsync
  • rtsp
  • sftp
  • ssh
  • tag
  • tel
  • telnet
  • urn
  • webcal
  • wtai
  • xmpp

Safe data URL content types

Note: This section is being discussed.

  • text/plain
  • image/gif
  • image/jpeg
  • image/png