withastro Astro up to 7.0.x View Transition CSS Generator transition.ts renderTransition cross site scripting

Summaryinfo

A vulnerability marked as problematic has been reported in withastro Astro up to 7.0.x. Affected is the function renderTransition of the file packages/astro/src/runtime/server/transition.ts of the component View Transition CSS Generator. The manipulation leads to cross site scripting. This vulnerability is uniquely identified as CVE-2026-73422. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability was found in withastro Astro up to 7.0.x. It has been rated as problematic. This issue affects the function renderTransition of the file packages/astro/src/runtime/server/transition.ts of the component View Transition CSS Generator. The manipulation with an unknown input leads to a cross site scripting vulnerability. Using CWE to declare the problem leads to CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Impacted is integrity. The summary by CVE is:

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.

It is possible to read the advisory at github.com. The identification of this vulnerability is CVE-2026-73422 since 08/12/2026. The exploitation is known to be easy. The attack may be initiated remotely. No form of authentication is needed for a successful exploitation. It demands that the victim is doing some kind of user interaction. Technical details of the vulnerability are known, but there is no available exploit. The attack technique deployed by this issue is T1059.007 according to MITRE ATT&CK.

Upgrading to version 7.1.0 eliminates this vulnerability.

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Productinfo

Vendor

• withastro

Name

• Astro

Version

• 7.0

Website

• Product: https://github.com/withastro/astro/

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