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GHSA-fw3g-2h3j-qmm7
No affected components available
Impact
Using carefully crafted input, an attacker may be able to sneak arbitrary HTML through Sanitize >= 5.0.0, < 6.0.1 when Sanitize is configured with a custom allowlist that allows noscript elements. This could result in XSS (cross-site scripting) or other undesired behavior when that HTML is rendered in a browser.
Sanitize's default configs don't allow noscript elements and are not vulnerable. This issue only affects users who are using a custom config that adds noscript to the element allowlist.
Patches
Sanitize >= 6.0.1 always removes noscript elements and their contents, even when noscript is in the allowlist.
Workarounds
Users who are unable to upgrade can prevent this issue by using one of Sanitize's default configs or by ensuring that their custom config does not include noscript in the element allowlist.
Details
The root cause of this issue is that HTML parsing rules treat the contents of a noscript element differently depending on whether scripting is enabled in the user agent. Nokogiri (the HTML parser Sanitize uses) doesn't support scripting so it follows the "scripting disabled" rules, but a web browser with scripting enabled will follow the "scripting enabled" rules. This means that Sanitize can't reliably make the contents of a noscript element safe for scripting enabled browsers. The safest thing to do is to remove the element and its contents entirely, which is now what Sanitize does in version 6.0.1 and later.
References
Credit
Thanks to David Klein from TU Braunschweig (@leeN) for reporting this issue.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. The attacker needs the user to perform some action, like clicking a link. The vulnerability can affect other systems as well, not just the initial system. There is a low impact on the confidentiality of the information. There is a low impact on the integrity of the data.
Exploitation attempts have been detected. Elevated vigilance and prompt remediation are advised.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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