GHSA-m85w-3h95-hcf9 is a medium-severity (CVSS 5.9) Cross-site Scripting (XSS) vulnerability in astro. A fix is available for astro — see the affected versions and patch details below.
DOM Clobbering Gadget found in astro's client-side router that leads to XSS
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for GHSA-m85w-3h95-hcf9.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-m85w-3h95-hcf9 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.
astronpmDescription
Summary
A DOM Clobbering gadget has been discoverd in Astro's client-side router. It can lead to cross-site scripting (XSS) in websites enables Astro's client-side routing and has stored attacker-controlled scriptless HTML elements (i.e., iframe tags with unsanitized name attributes) on the destination pages.
Details
Backgrounds
DOM Clobbering is a type of code-reuse attack where the attacker first embeds a piece of non-script, seemingly benign HTML markups in the webpage (e.g. through a post or comment) and leverages the gadgets (pieces of js code) living in the existing javascript code to transform it into executable code. More for information about DOM Clobbering, here are some references:
[1] https://scnps.co/papers/sp23_domclob.pdf [2] https://research.securitum.com/xss-in-amp4email-dom-clobbering/
Gadgets found in Astro
We identified a DOM Clobbering gadget in Astro's client-side routing module, specifically in the <ViewTransitions /> component. When integrated, this component introduces the following vulnerable code, which is executed during page transitions (e.g., clicking an <a> link):
However, this implementation is vulnerable to a DOM Clobbering attack. The document.scripts lookup can be shadowed by an attacker injected non-script HTML elements (e.g., <img name="scripts"><img name="scripts">) via the browser's named DOM access mechanism. This manipulation allows an attacker to replace the intended script elements with an array of attacker-controlled scriptless HTML elements.
The condition script.dataset.astroExec === '' on line 138 can be bypassed because the attacker-controlled element does not have a data-astroExec attribute. Similarly, the check on line 134 can be bypassed as the element does not require a type attribute.
Finally, the innerHTML of an attacker-injected non-script HTML elements, which is plain text content before, will be set to the .innerHTML of an script element that leads to XSS.
PoC
Consider a web application using Astro as the framework with client-side routing enabled and allowing users to embed certain scriptless HTML elements (e.g., form or iframe). This can be done through a bunch of website's feature that allows users to embed certain script-less HTML (e.g., markdown renderers, web email clients, forums) or via an HTML injection vulnerability in third-party JavaScript loaded on the page.
For PoC website, please refer to: https://stackblitz.com/edit/github-4xgj2d. Clicking the "about" button in the menu will trigger an alert(1) from an attacker-injected form element.
---
import Header from "../components/Header.astro";
import Footer from "../components/Footer.astro";
import { ViewTransitions } from "astro:transitions";
import "../styles/global.css";
const { pageTitle } = Astro.props;
---
<html lang="en">
<head>
<meta charset="utf-8" />
<link rel="icon" type="image/svg+xml" href="/favicon.svg" />
<meta name="viewport" content="width=device-width" />
<meta name="generator" content={Astro.generator} />
<title>{pageTitle}</title>
<ViewTransitions />
</head>
<body>
<!--USER INPUT-->
<iframe name="scripts">alert(1)</iframe>
<iframe name="scripts">alert(1)</iframe>
<!--USER INPUT-->
<Header />
<h1>{pageTitle}</h1>
<slot />
<Footer />
<script>
import "../scripts/menu.js";
</script>
</body>
</html>
Impact
This vulnerability can result in cross-site scripting (XSS) attacks on websites that built with Astro that enable the client-side routing with ViewTransitions and store the user-inserted scriptless HTML tags without properly sanitizing the name attributes on the page.
Patch
We recommend replacing document.scripts with document.getElementsByTagName('script') for referring to script elements. This will mitigate the possibility of DOM Clobbering attacks leveraging the name attribute.
Reference
Similar issues for reference:
- Webpack (CVE-2024-43788)
- Vite (CVE-2024-45812)
- layui (CVE-2024-47075)
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | astro | ≥ 3.0.0&&< 4.16.1 | 4.16.1npm install astro@4.16.1 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for astro, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update astro to 4.16.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-m85w-3h95-hcf9 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-m85w-3h95-hcf9 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-m85w-3h95-hcf9. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-m85w-3h95-hcf9 in your dependencies?
O3 Security finds GHSA-m85w-3h95-hcf9 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.