Bug 2514977 (CVE-2026-73422)

Summary: CVE-2026-73422 astro: Astro: Arbitrary code execution via unescaped View Transition animation properties
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in Astro. A remote attacker can exploit a reflected Cross-Site Scripting (XSS) vulnerability due to unescaped View Transition animation properties in the server-side CSS generator. By manipulating an animation value, such as 'duration', an attacker can inject arbitrary HTML or JavaScript. This allows for the execution of arbitrary JavaScript in the affected application's origin, potentially leading to access to sensitive page data and authenticated actions available to the victim.
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Bug Depends On: 2523529    
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Description OSIDB Bzimport 2026-08-12 20:41:24 UTC 
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.