CVE-2026-27902 Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers
Attackers can inject malicious scripts via unescaped error messages in Svelte SSR hydration markers, leading to XSS.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-27902?
CVE-2026-27902 is a medium-severity cross-site scripting vulnerability in sveltejs svelte, published on 26 Feb 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
Svelte performance oriented web framework. Prior to version 5.53.5, errors from `transformError` were not correctly escaped prior to being embedded in the HTML output, causing potential HTML injection and XSS if attacker-controlled content is returned from `transformError`. Version 5.53.5 fixes the issue.
Weakness: CWE-79
Which versions are affected by CVE-2026-27902?
2 open source packages ship an affected version, including svelte. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
svelte npm | From 5.53.0 | 5.53.5 |
svelte npm | From 5.53.0 | 5.53.5 |
Products include Svelte Svelte.
How do I fix CVE-2026-27902?
Upgrade svelte to 5.53.5 or later.
Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.
Is CVE-2026-27902 being exploited?
There is no known exploitation of CVE-2026-27902 in the wild and no public exploit code.
Other vulnerabilities in sveltejs svelte
- CVE-2021-29261 Code injection in n/a
- CVE-2026-42567 Svelte: ReDoS in `<svelte:element>` Tag Validation
- CVE-2024-45047 Potential mXSS vulnerability due to improper HTML escaping in svelte
- CVE-2022-25875 Cross-site Scripting (XSS)
- CVE-2026-42573 Svelte: XSS via DOM Clobbering of Internal Framework State
Sources
Also known as GHSA-qgvg-pr8v-6rr3.