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Medium, CVSS 5.3amended

Astro: Reflected XSS via unescaped View Transition animation properties

CVE-2026-73422GHSA-4g3v-8h47-v7g6

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (astro 7.1.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • npm astro

    Affected
    >= 2.9.0, <= 7.0.9
    Fixed in
    7.1.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
5.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source
EPSS
  • CVE-2026-73422: 0.55% estimated exploitation activity in the next 30 days; percentile 45.91 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Summary Astro's server-side View Transition CSS generator interpolates animation properties into an inline <style element without escaping them for the CSS and HTML contexts. An attacker-controlled value passed to an animation property such as duration can contain a </style sequence, terminate the generated style element, and inject arbitrary HTML or JavaScript. This is similar to GHSA-8hv8-536x-4wqp, but exploits a different injection point: unescaped View Transition animation values in a server-generated <style element rather than an unescaped slot name in a hydration template. Like GHSA-8hv8-536x-4wqp, exploitation requires an application to pass attacker-controlled data to an Astro API. However, the value is subsequently inserted into the HTML response without context-appropriate escaping by Astro. Details packages/astro/src/runtime/server/transition.ts The generated stylesheet is wrapped in a <style element and marked as HTML-safe: Animation properties are added to the…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-4g3v-8h47-v7g6

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-4g3v-8h47-v7g6

Agent brief

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# Patch Next advisory brief: CVE-2026-73422

Advisory: Astro: Reflected XSS via unescaped View Transition animation properties
IDs: CVE-2026-73422, GHSA-4g3v-8h47-v7g6
Record: https://patchnext.com/advisories/cve-2026-73422 (revision 3, source checked 26 Oct 2026, 13:01 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: astro 7.1.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm astro: affected >= 2.9.0, <= 7.0.9; fixed in 7.1.0

## 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-4g3v-8h47-v7g6 (OSV record GHSA-4g3v-8h47-v7g6 lists affected ranges: npm astro >=2.9.0 <7.1.0 (fixed))
- Verified: https://github.com/advisories/GHSA-4g3v-8h47-v7g6 (GitHub-reviewed advisory GHSA-4g3v-8h47-v7g6 lists affected ranges: npm astro >=2.9.0 <=7.0.9)

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