CVE-2022-36033

jsoup may incorrectly sanitize HTML including `javascript:` URL expressions, which could allow cross-site scripting (XSS) attacks when a reader subsequently clicks that link. If the non-default `SafeList.preserveRelativeLinks` option is enabled, HTML including `javascript:` URLs that have been crafted with control characters will not be sanitized. If the site that this HTML is published on does not set a Content Security Policy, an XSS attack is then possible. ### Impact Sites that accept input HTML from users and use jsoup to sanitize that HTML, may be vulnerable to cross-site scripting (XSS) attacks, if they have enabled `SafeList.preserveRelativeLinks` and do not set an appropriate Content Security Policy. ### Patches This issue is patched in jsoup 1.15.3. Users should upgrade to this version. Additionally, as the unsanitized input may have been persisted, old content should be cleaned again using the updated version. ### Workarounds To remediate this issue without immediately upgrading: - disable `SafeList.preserveRelativeLinks`, which will rewrite input URLs as absolute URLs - ensure an appropriate [Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) is defined. (This should be used regardless of upgrading, as a defence-in-depth best practice.) ### Background and root cause jsoup includes a [Cleaner](https://jsoup.org/apidocs/org/jsoup/safety/Cleaner.html) component, which is designed to [sanitize input HTML](https://jsoup.org/cookbook/cleaning-html/safelist-sanitizer) against configurable safe-lists of acceptable tags, attributes, and attribute values. This includes removing potentially malicious attributes such as `<a href="javascript:...">`, which may enable XSS attacks. It does this by validating URL attributes against allowed URL protocols (e.g. `http`, `https`). However, an attacker may be able to bypass this check by embedding control characters into the href attribute value. This causes the Java URL class, which is used to resolve relative URLs to absolute URLs before checking the URL's protocol, to treat the URL as a relative URL. It is then resolved into an absolute URL with the configured base URI. For example, `java\tscript:...` would resolve to `https://example.com/java\tscript:...`. By default, when using a safe-list that allows `a` tags, jsoup will rewrite any relative URLs (e.g. `/foo/`) to an absolute URL (e.g. `https://example.com/foo/`). Therefore, this attack attempt would be successfully mitigated. However, if the option [SafeList.preserveRelativeLinks](https://jsoup.org/apidocs/org/jsoup/safety/Safelist.html#preserveRelativeLinks(boolean)) is enabled (which does not rewrite relative links to absolute), the input is left as-is. While Java will treat a path like `java\tscript:` as a relative path, as it does not match the allowed characters of a URL spec, browsers may normalize out the control characters, and subsequently evaluate it as a `javascript:` spec inline expression. That disparity then leads to an XSS opportunity. Sites defining a Content Security Policy that does not allow javascript expressions in link URLs will not be impacted, as the policy will prevent the script's execution. ### For more information If you have any questions or comments about this advisory: * Open an issue in [jsoup](https://github.com/jhy/jsoup) * Email the author of jsoup at [[email protected]](mailto:[email protected]) ### Credits Thanks to Jens Häderer, who reported this issue, and contributed to its resolution.

jsoup may incorrectly sanitize HTML including `javascript:` URL expressions, which could allow cross-site scripting (XSS) attacks when a reader subsequently clicks that link. If the non-default `SafeList.preserveRelativeLinks` option is enabled, HTML including `javascript:` URLs that have been crafted with control characters will not be sanitized. If the site that this HTML is published on does not set a Content Security Policy, an XSS attack is then possible. ### Impact Sites that accept input HTML from users and use jsoup to sanitize that HTML, may be vulnerable to cross-site scripting (XSS) attacks, if they have enabled `SafeList.preserveRelativeLinks` and do not set an appropriate Content Security Policy. ### Patches This issue is patched in jsoup 1.15.3. Users should upgrade to this version. Additionally, as the unsanitized input may have been persisted, old content should be cleaned again using the updated version. ### Workarounds To remediate this issue without immediately upgrading: - disable `SafeList.preserveRelativeLinks`, which will rewrite input URLs as absolute URLs - ensure an appropriate [Content Security Policy](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) is defined. (This should be used regardless of upgrading, as a defence-in-depth best practice.) ### Background and root cause jsoup includes a [Cleaner](https://jsoup.org/apidocs/org/jsoup/safety/Cleaner.html) component, which is designed to [sanitize input HTML](https://jsoup.org/cookbook/cleaning-html/safelist-sanitizer) against configurable safe-lists of acceptable tags, attributes, and attribute values. This includes removing potentially malicious attributes such as `<a href="javascript:...">`, which may enable XSS attacks. It does this by validating URL attributes against allowed URL protocols (e.g. `http`, `https`). However, an attacker may be able to bypass this check by embedding control characters into the href attribute value. This causes the Java URL class, which is used to resolve relative URLs to absolute URLs before checking the URL's protocol, to treat the URL as a relative URL. It is then resolved into an absolute URL with the configured base URI. For example, `java\tscript:...` would resolve to `https://example.com/java\tscript:...`. By default, when using a safe-list that allows `a` tags, jsoup will rewrite any relative URLs (e.g. `/foo/`) to an absolute URL (e.g. `https://example.com/foo/`). Therefore, this attack attempt would be successfully mitigated. However, if the option [SafeList.preserveRelativeLinks](https://jsoup.org/apidocs/org/jsoup/safety/Safelist.html#preserveRelativeLinks(boolean)) is enabled (which does not rewrite relative links to absolute), the input is left as-is. While Java will treat a path like `java\tscript:` as a relative path, as it does not match the allowed characters of a URL spec, browsers may normalize out the control characters, and subsequently evaluate it as a `javascript:` spec inline expression. That disparity then leads to an XSS opportunity. Sites defining a Content Security Policy that does not allow javascript expressions in link URLs will not be impacted, as the policy will prevent the script's execution. ### For more information If you have any questions or comments about this advisory: * Open an issue in [jsoup](https://github.com/jhy/jsoup) * Email the author of jsoup at [[email protected]](mailto:[email protected]) ### Credits Thanks to Jens Häderer, who reported this issue, and contributed to its resolution.

jsoup es un analizador HTML de Java, construido para la edición, limpieza y raspado de HTML, y para la seguridad de vulnerabilidades de tipo cross-site scripting (XSS). jsoup puede sanear incorrectamente el HTML que incluye expresiones URL "javascript:", lo que podría permitir ataques de tipo XSS cuando un lector hace clic posteriormente en ese enlace. Si la opción no predeterminada "SafeList.preserveRelativeLinks" está habilitada, el HTML que incluya expresiones URL "javascript:" que hayan sido diseñadas con caracteres de control no será saneado. Si el sitio en el que es publicado este HTML no establece una política de seguridad de contenidos, es posible un ataque de tipo XSS. Este problema ha sido corregido en jsoup versión 1.15.3. Los usuarios deberían actualizar a esta versión. Además, como es posible que la entrada no saneada haya sido mantenido, el contenido antiguo debe limpiarse de nuevo usando la versión actualizada. Para mitigar este problema sin tener que actualizar inmediatamente - deshabilite "SafeList.preserveRelativeLinks", que reescribirá las URLs de entrada como URLs absolutas - asegúrese de que es definido una [Política de Seguridad de Contenidos](https://developer.mozilla.org/en-US/docs/Web/HTTP/CSP) apropiada. (Esto debería usarse independientemente de la actualización, como mejor práctica de defensa en profundidad)