How severe is CVE-2025-55303?

No CVSS score has been assigned to CVE-2025-55303 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2025-55303?

CVE-2025-55303 affects the following packages: astro (npm), @astrojs/node (npm), astro (npm). Ecosystems affected: npm.

How do I fix CVE-2025-55303?

Update astro to 5.13.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-55303 is resolved across your whole dependency graph.

How do I detect CVE-2025-55303 in my npm dependencies?

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.

How do I mitigate CVE-2025-55303 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2025-55303 actively exploited in the wild?

No public exploit code has been indexed for CVE-2025-55303 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2025-55303?

CVE-2025-55303 has an EPSS (Exploit Prediction Scoring System) score of 0.7%, placing it in the 52th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2025-55303?

CVE-2025-55303 is classified as Cross-site Scripting (XSS) (CWE-79), CWE-115 (CWE-115). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

Is there exploit tooling available for CVE-2025-55303?

A Nuclei detection template exists for CVE-2025-55303, meaning automated scanners can fingerprint it. Public exploit tooling significantly increases real-world risk — prioritize patching and ensure detection coverage. Exploit tooling should only ever be used in isolated, authorized testing environments.

When was CVE-2025-55303 published, and has it been updated?

CVE-2025-55303 was published on August 19, 2025 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦 npm

Not in CISA KEV

CVE-2025-55303 — astro

Fix: withastro/astro@4d16de7

CVE-2025-55303 is a Cross-site Scripting (XSS) vulnerability in astro. A fix is available for astro — see the affected versions and patch details below.

Unauthorized third-party images in Astro’s _image endpoint

Also known asGHSA-xf8x-j4p2-f749

Published

Aug 19, 2025

Updated

Oct 28, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

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.
CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for CVE-2025-55303.

EPSS Exploitation Probability

via FIRST.org ↗

0.7%probability of exploitation in next 30 days

Lower Risk+0.04%

Lower risk than most CVEs52th percentile — riskier than 52% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

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.

735other npm packages depend on this — each one inherits the vulnerability until it's patched upstream

astronpm

11.7Mdownloads / week

@astrojs/nodenpm

1.4Mdownloads / week

Description

Summary

In affected versions of astro, the image optimization endpoint in projects deployed with on-demand rendering allows images from unauthorized third-party domains to be served.

Details

On-demand rendered sites built with Astro include an /_image endpoint which returns optimized versions of images.

The /_image endpoint is restricted to processing local images bundled with the site and also supports remote images from domains the site developer has manually authorized (using the image.domains or image.remotePatterns options).

However, a bug in impacted versions of astro allows an attacker to bypass the third-party domain restrictions by using a protocol-relative URL as the image source, e.g. /_image?href=//example.com/image.png.

Proof of Concept

Create a new minimal Astro project ([email protected]).

Configure it to use the Node adapter (@astrojs/[email protected] — newer versions are not impacted):

// astro.config.mjs
import { defineConfig } from 'astro/config';
import node from '@astrojs/node';

export default defineConfig({
	adapter: node({ mode: 'standalone' }),
});

Build the site by running astro build.
Run the server, e.g. with astro preview.
Append /_image?href=//placehold.co/600x400 to the preview URL, e.g. http://localhost:4321/_image?href=//placehold.co/600x400
The site will serve the image from the unauthorized placehold.co origin.

Impact

Allows a non-authorized third-party to create URLs on an impacted site’s origin that serve unauthorized image content. In the case of SVG images, this could include the risk of cross-site scripting (XSS) if a user followed a link to a maliciously crafted SVG.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`astro`	≥ 5.0.0-alpha.0&&< 5.13.2	5.13.2`npm install astro@5.13.2`
📦npm	`@astrojs/node`	all versions	9.1.1`npm install @astrojs/node@9.1.1`
📦npm	`astro`	all versions	4.16.19`npm install astro@4.16.19`

Affected Products

1 product · 2 configurations

Application

astroastro

≥ 5.0.0 && < 5.13.2

range

Detection & mitigation playbook

Open-source dependency

Detect
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 5.13.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2025-55303 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

How to detect CVE-2025-55303

A community-maintained Nuclei template exists for this CVE. You can scan for it directly:

nuclei -id cve-2025-55303 -u https://target

Template: Astro - Unauthorized Third-Party Image Access
Severity: medium
Impact: Attackers can serve images from unauthorized third-party domains, potentially leading to information disclosure or content spoofing.
Remediation: Update to versions 5.13.2 or 4.16.18 or later.

Template by ProjectDiscovery nuclei-templates (theamanrawat), MIT licensed. View the full template. Scan only systems you are authorised to test.

Frequently Asked Questions

### Summary In affected versions of `astro`, the image optimization endpoint in projects deployed with on-demand rendering allows images from unauthorized third-party domains to be served. ### Details On-demand rendered sites built with Astro include an `/_image` endpoint which returns optimized versions of images. The `/_image` endpoint is restricted to processing local images bundled with the site and also supports remote images from domains the site developer has manually authorized (using the [`image.domains`](https://docs.astro.build/en/reference/configuration-reference/#imagedomains)

O3 Security · Impact-Aware SCA

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