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HTML sanitization

From Wikipedia, the free encyclopedia

Indata sanitization,HTML sanitizationis the process of examining anHTMLdocument and producing a new HTML document that preserves only whatever tags and attributes are designated "safe" and desired. HTML sanitization can be used to protect against attacks such ascross-site scripting(XSS) by sanitizing any HTML code submitted by a user.

Details

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Basic tags for changing fonts are often allowed, such as<b>,<i>,<u>,<em>,and<strong>while more advanced tags such as<script>,<object>,<embed>,and<link>are removed by the sanitization process. Also potentially dangerousattributessuch as theonclickattribute are removed in order to prevent malicious code from being injected.

Sanitization is typically performed by using either awhitelistor ablacklistapproach. Leaving a safe HTML element off a whitelist is not so serious; it simply means that that feature will not be included post-sanitation. On the other hand, if an unsafe element is left off a blacklist, then the vulnerability will not be sanitized out of the HTML output. An out-of-date blacklist can therefore be dangerous if new, unsafe features have been introduced to the HTML Standard.

Further sanitization can be performed based on rules which specify what operation is to be performed on the subject tags. Typical operations include removal of the tag itself while preserving the content, preserving only the textual content of a tag or forcing certain values on attributes.[1]

Implementations

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InPHP,HTML sanitization can be performed using thestrip_tags()function at the risk of removing all textual content following an unclosed less-than symbol or angle bracket.[2]The HTML Purifier library is another popular option for PHP applications.[3]

InJava(and.NET), sanitization can be achieved by using theOWASPJava HTML Sanitizer Project.[4]

In.NET,a number of sanitizers use the Html Agility Pack, an HTML parser.[5][6][1]Another library is HtmlSanitizer.[7]

InJavaScriptthere are "JS-only" sanitizers for theback end,and browser-based[8]implementations that use browser's ownDocument Object Model(DOM) parser to parse the HTML (for better performance).

References

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  1. ^ab"HtmlRuleSanitizer".GitHub.13 August 2021.
  2. ^"strip_tags".PHP.NET.
  3. ^"HTML Purifier - Filter your HTML the standards-compliant way!".htmlpurifier.org.
  4. ^"OWASP Java HTML Sanitizer".
  5. ^"HTML Agility Pack - Home".Archived fromthe originalon 2013-01-01.Retrieved2013-01-04.
  6. ^"Whitelist santize with HtmlAgilityPack".14 June 2011.
  7. ^Ganss, Michael (5 December 2023)."HtmlSanitizer".Retrieved7 December2023.
  8. ^"JS HTML Sanitizer".GitHub.14 October 2021.