Astro: XSS via Unescaped Attribute Names in Spread Props

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.2 · CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:L/I:L/A:N

EPSS

• CVE-2026-54298: 0.23% estimated exploitation activity in the next 30 days; percentile 13.61 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The spreadAttributes function in Astro's server-side rendering pipeline iterates over object keys and passes them directly to addAttribute, which interpolates the key into the HTML output without escaping. When a developer uses the spread syntax {...props} on an HTML element and the object keys come from an untrusted source (API, CMS, URL parameters), an attacker can inject arbitrary HTML attributes including event handlers like onmousemove, onclick, or break out of the attribute context entirely to inject new elements. Details The vulnerable function is addAttribute at packages/astro/src/runtime/server/render/util.ts:81-141: This function is called from spreadAttributes at packages/astro/src/runtime/server/index.ts:91-92: The toAttributeString function escapes the attribute value, but the attribute name key is never validated or escaped. An attacker can craft a JSON object with a key containing " characters to break out of the attribute context and inject event handlers.…

Published by the source

16 Jun 2026, 14:57 UTC

Last modified by the source

18 Jul 2026, 17:30 UTC

Source last checked

26 Oct 2026, 12:57 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-jrpj-wcv7-9fh9

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-jrpj-wcv7-9fh9

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# Patch Next advisory brief: CVE-2026-54298

Advisory: Astro: XSS via Unescaped Attribute Names in Spread Props
IDs: CVE-2026-54298, GHSA-jrpj-wcv7-9fh9
Record: https://patchnext.com/advisories/cve-2026-54298 (revision 2, source checked 26 Oct 2026, 12:57 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: astro 6.4.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm astro: affected < 6.4.6; fixed in 6.4.6

## Suggested inspection (read-only)
- `npm ls astro --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on astro.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-jrpj-wcv7-9fh9 (OSV record GHSA-jrpj-wcv7-9fh9 lists affected ranges: npm astro >=0 <6.4.6 (fixed))
- Verified: https://github.com/advisories/GHSA-jrpj-wcv7-9fh9 (GitHub-reviewed advisory GHSA-jrpj-wcv7-9fh9 lists affected ranges: npm astro >=0 <6.4.6)

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