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Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')


Severity Medium
Score 6.1/10


Bleach before 3.1.1 has a mutation-based XSS (mXSS) vulnerability when noscript tag is allowed in addition to one of the following tags: title, textarea, script, style, noembed, noframes, iframe, xmp or comment. This occurs due to bleach utilizing its parser, html5lib, with scripting=False. In this case, the data of the noscript tags will be parsed as HTML, while the browser parses them as rawdata. This can cause arbitrary HTML and JavaScript codes to run on the victim's browser.

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  • NONE
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CWE-79 - Cross Site Scripting

Cross-Site Scripting, commonly referred to as XSS, is the most dominant class of vulnerabilities. It allows an attacker to inject malicious code into a pregnable web application and victimize its users. The exploitation of such a weakness can cause severe issues such as account takeover, and sensitive data exfiltration. Because of the prevalence of XSS vulnerabilities and their high rate of exploitation, it has remained in the OWASP top 10 vulnerabilities for years.

Advisory Timeline

  • Published