Astro: Reflected XSS via unescaped View Transition animation properties (CVE-2026-73422) | HOL Guard CVE

Medium · CVSS 5.3CVE-2026-73422GHSA-4G3V-8H47-V7G6

Astro: Reflected XSS via unescaped View Transition animation properties

Answer in brief

CVE-2026-73422 records a Medium severity (CVSS 5.3) vulnerability in Astro: Reflected XSS via unescaped View Transition animation properties. The current sources do not mark it as known exploited. The current feed maps withastro/astro (generic), astro (npm), astro (npm). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Aug 12, 2026Updated Sep 9, 2026Source checked Sep 29, 2026First seen by HOL Aug 12, 2026Material review Sep 9, 2026

Upstream Advisory

Key facts

Risk: Medium · CVSS 5.3
Exploitation: Not marked as known exploited
Affected software: 3 mapped packages or products
Fix availability: Available

Why this deserves its current priority

CVSS is 5.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps withastro/astro (generic), astro (npm), astro (npm). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
withastro/astrogeneric	>= 2.9.0, < 7.1.0	Not reported
astronpm	>=2.9.0 <7.1.0	7.1.0
astronpm	>=2.9.0,<=7.0.9	7.1.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for withastro/astro, astro, astro.
Review the reported fix. Update astro to 7.1.0; astro to 7.1.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Aug 12, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 9, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Aug 12, 2026

Sources and claim methodology

Upstream source description

Astro is a web framework for content-driven websites. From 2.9.0 until 7.1.0, Astro's server-side View Transition CSS generator interpolates animation properties into an inline style element without escaping them for CSS and HTML contexts. An attacker-controlled View Transition animation value such as duration can terminate the generated style element and inject arbitrary HTML or JavaScript. The affected code is packages/astro/src/runtime/server/transition.ts; renderTransition passes sheet.toString() into markHTMLString(), while addAnimationProperty serializes duration through toTimeValue() and also handles easing, direction, delay, fillMode, and name. Exploitation requires an on-demand or server-rendered route to pass attacker-controlled data into a View Transition animation definition and can execute arbitrary JavaScript in the affected application's origin, allowing access to sensitive page data and authenticated actions available to the victim. This issue is fixed in version 7.1.0.

Quoted source text, attributed separately from HOL analysis.