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Medium, CVSS 5.1amended

Astro: XSS via unescaped spread attribute names in renderHTMLElement (incomplete fix for CVE-2026-54298)

CVE-2026-59729GHSA-f48w-9m4c-m7f5

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (astro 7.0.6), 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
    < 7.0.6
    Fixed in
    7.0.6

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
5.1 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N · score source
EPSS
  • CVE-2026-59729: 0.47% estimated exploitation activity in the next 30 days; percentile 40.99 (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 The fix for CVE-2026-54298 (GHSA-jrpj-wcv7-9fh9) added an INVALIDATTRNAMECHAR guard to addAttribute() so that spread-prop attribute names containing "' /= or whitespace are dropped. A second attribute-rendering path, renderHTMLElement() in packages/astro/src/runtime/server/render/dom.ts, has its own inline attribute loop that does not go through addAttribute() and was not updated. It interpolates the attribute name unescaped and only escapes the value, so untrusted prop keys spread onto a native-HTMLElement-subclass component can still break out of the attribute context, resulting in XSS. Details renderHTMLElement builds attributes directly: The attribute name (attr) is interpolated raw; only the value is escaped via toAttributeString. By contrast, the hardened addAttribute in util.ts rejects invalid names: renderHTMLElement is reached from component.ts when the component is a native HTMLElement subclass: where props carries spread props verbatim. Reachability The branch only…

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

    Amended from ghsa record GHSA-f48w-9m4c-m7f5

  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-f48w-9m4c-m7f5

Agent brief

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# Patch Next advisory brief: CVE-2026-59729

Advisory: Astro: XSS via unescaped spread attribute names in renderHTMLElement (incomplete fix for CVE-2026-54298)
IDs: CVE-2026-59729, GHSA-f48w-9m4c-m7f5
Record: https://patchnext.com/advisories/cve-2026-59729 (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 5.1)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: astro 7.0.6. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm astro: affected < 7.0.6; fixed in 7.0.6

## 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-f48w-9m4c-m7f5 (OSV record GHSA-f48w-9m4c-m7f5 lists affected ranges: npm astro >=0 <7.0.6 (fixed))
- Verified: https://github.com/advisories/GHSA-f48w-9m4c-m7f5 (GitHub-reviewed advisory GHSA-f48w-9m4c-m7f5 lists affected ranges: npm astro >=0 <7.0.6)

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