CVE-2026-27696

changedetection.io is a free open source web page change detection tool. In versions prior to 0.54.1, changedetection.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. The 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. Version 0.54.1 contains a fix for the issue.

changedetection.io is a free open source web page change detection tool. In versions prior to 0.54.1, changedetection.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. The 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. Version 0.54.1 contains a fix for the issue.

Summary

Changedetection.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:

• http://169.254.169.254
• http://10.0.0.1/
• http://127.0.0.1/

The 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.

This is particularly severe because:

• The fetched content is stored and viewable - this is not a blind SSRF
• Watches are fetched periodically - creating a persistent SSRF that continuously accesses internal resources
• By default, no password is set - the web UI is accessible without authentication
• Self-hosted deployments typically run on cloud infrastructure where 169.254.169.254 returns real IAM credentials

Details

The 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:

# changedetectionio/validate_url.py:60-122
@lru_cache(maxsize=1000)
def is_safe_valid_url(test_url):

    safe_protocol_regex = '^(http|https|ftp):'

    # Check protocol
    pattern = re.compile(os.getenv('SAFE_PROTOCOL_REGEX', safe_protocol_regex), re.IGNORECASE)
    if not pattern.match(test_url.strip()):
        return False

    # Check URL format
    if not validators.url(test_url, simple_host=True):
        return False

    return True  # No IP address validation performed

The HTTP fetcher in changedetectionio/content_fetchers/requests.py (lines 83–89) then makes the request without any additional IP validation:

# changedetectionio/content_fetchers/requests.py:83-89
r = session.request(method=request_method,
                    url=url,            # User-provided URL, no IP validation
                    headers=request_headers,
                    timeout=timeout,
                    proxies=proxies,
                    verify=False)

The response content is stored and made available to the user:

# changedetectionio/content_fetchers/requests.py:140-142
self.content = r.text     # Text content stored
self.raw_content = r.content  # Raw bytes stored

This validation gap exists in all entry points that accept watch URLs:

• Web UI: changedetectionio/store/__init__.py:718
• REST API: changedetectionio/api/watch.py:163, 428
• Import API: changedetectionio/api/import.py:188

All use the same is_safe_valid_url() function, so a single fix addresses all paths.

PoC

Prerequisites

• A changedetection.io instance (Docker deployment)
• Network access to the instance (default port 5000)

Step 1: Deploy changedetection.io with an internal service

Create internal-service.py:

#!/usr/bin/env python3
from http.server import HTTPServer, BaseHTTPRequestHandler
import json
class H(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.send_header('Content-Type', 'application/json')
        self.end_headers()
        self.wfile.write(json.dumps({
            'Code': 'Success',
            'AccessKeyId': 'AKIAIOSFODNN7EXAMPLE',
            'SecretAccessKey': 'wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY',
            'Token': 'FwoGZXIvYXdzEBYaDExampleSessionToken'
        }).encode())
HTTPServer(('0.0.0.0', 80), H).serve_forever()

Create Dockerfile.internal:

FROM python:3.11-slim
COPY internal-service.py /server.py
CMD ["python3", "/server.py"]

Create docker-compose.yml:

version: "3.8"
services:
  changedetection:
    image: ghcr.io/dgtlmoon/changedetection.io
    ports:
      -…

changedetection.io is a free open source web page change detection tool. In versions prior to 0.54.1, changedetection.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. The 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. Version 0.54.1 contains a fix for the issue.

changedetection.io is a free open source web page change detection tool. In versions prior to 0.54.1, changedetection.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. The 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. Version 0.54.1 contains a fix for the issue.

Summary

Changedetection.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:

• http://169.254.169.254
• http://10.0.0.1/
• http://127.0.0.1/

The 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.

This is particularly severe because:

• The fetched content is stored and viewable - this is not a blind SSRF
• Watches are fetched periodically - creating a persistent SSRF that continuously accesses internal resources
• By default, no password is set - the web UI is accessible without authentication
• Self-hosted deployments typically run on cloud infrastructure where 169.254.169.254 returns real IAM credentials

Details

The 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:

# changedetectionio/validate_url.py:60-122
@lru_cache(maxsize=1000)
def is_safe_valid_url(test_url):

    safe_protocol_regex = '^(http|https|ftp):'

    # Check protocol
    pattern = re.compile(os.getenv('SAFE_PROTOCOL_REGEX', safe_protocol_regex), re.IGNORECASE)
    if not pattern.match(test_url.strip()):
        return False

    # Check URL format
    if not validators.url(test_url, simple_host=True):
        return False

    return True  # No IP address validation performed

The HTTP fetcher in changedetectionio/content_fetchers/requests.py (lines 83–89) then makes the request without any additional IP validation:

# changedetectionio/content_fetchers/requests.py:83-89
r = session.request(method=request_method,
                    url=url,            # User-provided URL, no IP validation
                    headers=request_headers,
                    timeout=timeout,
                    proxies=proxies,
                    verify=False)

The response content is stored and made available to the user:

# changedetectionio/content_fetchers/requests.py:140-142
self.content = r.text     # Text content stored
self.raw_content = r.content  # Raw bytes stored

This validation gap exists in all entry points that accept watch URLs:

• Web UI: changedetectionio/store/__init__.py:718
• REST API: changedetectionio/api/watch.py:163, 428
• Import API: changedetectionio/api/import.py:188

All use the same is_safe_valid_url() function, so a single fix addresses all paths.

PoC

Prerequisites

• A changedetection.io instance (Docker deployment)
• Network access to the instance (default port 5000)

Step 1: Deploy changedetection.io with an internal service

Create internal-service.py:

#!/usr/bin/env python3
from http.server import HTTPServer, BaseHTTPRequestHandler
import json
class H(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.send_header('Content-Type', 'application/json')
        self.end_headers()
        self.wfile.write(json.dumps({
            'Code': 'Success',
            'AccessKeyId': 'AKIAIOSFODNN7EXAMPLE',
            'SecretAccessKey': 'wJalrXUtnFEMI/K7MDENG/bPxRfiCYEXAMPLEKEY',
            'Token': 'FwoGZXIvYXdzEBYaDExampleSessionToken'
        }).encode())
HTTPServer(('0.0.0.0', 80), H).serve_forever()

Create Dockerfile.internal:

FROM python:3.11-slim
COPY internal-service.py /server.py
CMD ["python3", "/server.py"]

Create docker-compose.yml:

version: "3.8"
services:
  changedetection:
    image: ghcr.io/dgtlmoon/changedetection.io
    ports:
      -…

changedetection.io is a free open source web page change detection tool. In versions prior to 0.54.1, changedetection.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. The 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. Version 0.54.1 contains a fix for the issue.