CVE-2024-45047: Potential mXSS vulnerability due to improper HTML escaping in svelte
Summary
A potential XSS vulnerability exists in Svelte for versions prior to 4.2.19.
Details
Svelte improperly escapes HTML on server-side rendering. It converts strings according to the following rules:
- If the string is an attribute value: - " -> " - & -> & - Other characters -> No conversion - Otherwise: - < -> < - & -> & - Other characters -> No conversion
The assumption is that attributes will always stay as such, but in some situation the final DOM tree rendered on browsers is different from what Svelte expects on server-side rendering. This may be leveraged to perform XSS attacks. More specifically, this can occur when injecting malicious content into an attribute within a <noscript> tag.
PoC
A vulnerable page (+page.svelte): html <script> import { page } from "$app/stores"
// user input let href = $page.url.searchParams.get("href") ?? "https://example.com"; </script>
<noscript> <a href={href}>test</a> </noscript>
If a user accesses the following URL, http://localhost:4173/?href=</noscript><script>alert(123)</script> then, alert(123) will be executed.
Impact
XSS, when using an attribute within a noscript tag
Other sources
svelte performance oriented web framework. A potential mXSS vulnerability exists in Svelte for versions up to but not including 4.2.19. Svelte improperly escapes HTML on server-side rendering. The assumption is that attributes will always stay as such, but in some situation the final DOM tree rendered on browsers is different from what Svelte expects on server-side rendering. This may be leveraged to perform XSS attacks, and a type of the XSS is known as mXSS (mutation XSS). More specifically, this can occur when injecting malicious content into an attribute within a noscript tag. This issue has been addressed in release version 4.2.19. Users are advised to upgrade. There are no known workarounds for this vulnerability.
— MITRE
Affected Software
Event History
Frequently Asked Questions
What is the severity of CVE-2024-45047?
CVE-2024-45047 is classified as a moderate severity vulnerability due to its potential for XSS attacks under specific conditions.
How do I fix CVE-2024-45047?
To fix CVE-2024-45047, upgrade to Svelte version 4.2.19 or later.
Which versions of Svelte are affected by CVE-2024-45047?
CVE-2024-45047 affects all versions of Svelte prior to 4.2.19.
What type of vulnerability is CVE-2024-45047?
CVE-2024-45047 is an XSS (Cross-Site Scripting) vulnerability.
Is server-side rendering impacted by CVE-2024-45047?
Yes, CVE-2024-45047 arises from improper HTML escaping during server-side rendering in Svelte.