GHSA-vffh-c9pq-4crh: Uptime kuma Uptime Kuma Server-side Template Injection Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-vffh-c9pq-4crh",
  "modified" : "2025-10-20T20:03:15Z",
  "published" : "2025-10-20T20:03:15Z",
  "aliases" : [ ],
  "summary" : "Uptime Kuma Server-side Template Injection (SSTI) in Notification Templates Allows Arbitrary File Read",
  "details" : "### Summary\n\nIn some Notification types (e.g., Webhook, Telegram), the `send()` function allows user-controlled renderTemplate input. This leads to a Server-side Template Injection (SSTI) vulnerability that can be exploited to read arbitrary files from the server.\n\n\n\n### Details\n\nThe root cause is how Uptime Kuma renders user-controlled templates via `renderTemplate()`. The function instantiates a Liquid template engine and parses the `template` argument without sanitization:\n\n```js\nasync renderTemplate(template, msg, monitorJSON, heartbeatJSON) {\n    const engine = new Liquid();\n    const parsedTpl = engine.parse(template);\n\n    // ...\n}\n```\n\nIn some Notification flows, the `send()` implementation passes user-editable fields directly into `renderTemplate()`:\n```js\n// webhook.js\nif (notification.webhookContentType === \"form-data\") {\n    const formData = new FormData();\n    formData.append(\"data\", JSON.stringify(data));\n    config.headers = formData.getHeaders();\n    data = formData;\n} else if (notification.webhookContentType === \"custom\") {\n    data = await this.renderTemplate(notification.webhookCustomBody, msg, monitorJSON, heartbeatJSON); //<- this line cause SSTI\n}\n```\n\nBecause `notification` can be edited by users and is rendered by the Liquid engine without proper sandboxing or a whitelist of allowed operations, an attacker can supply a crafted template that causes the server to read arbitrary files. In particular, Liquid’s template tags (e.g. `{% render ... %}`) can be abused to include server-side files if the engine is not restricted, resulting in Server-side Template Injection (SSTI) that leaks sensitive file contents.\n\n\n\n### PoC\n\n1. Open Uptime Kuma → **Notifications** → **Add** or **Edit** an existing Webhook notification.\n2. Set notification type to **Webhook** and set **Request Body**  to **Custom Body**.\n3. Paste the following JSON into the custom request body:\n\n```json\n{\n  \"Title\": {% render '/etc/passwd' %}\n}\n```\n\n4. Click test.\n5. Your webhook will receive the file content\n\n\n\n### Impact\n\nThis is a post-authentication Server-side Template Injection (SSTI) vulnerability that allows an authenticated user to perform arbitrary file read on the server.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "npm",
      "name" : "uptime-kuma"
    },
    "versions" : [ "2.0.0-dev.0" ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/louislam/uptime-kuma/security/advisories/GHSA-vffh-c9pq-4crh"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/louislam/uptime-kuma"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-1336", "CWE-36" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2025-10-20T20:03:15Z",
    "nvd_published_at" : null
  }
}