IP Spoofing Bypass in HedgeDoc Rate Limiting

Executive Summary

HedgeDoc is an open-source application for real-time collaborative markdown notes. The vulnerability in versions prior to 1.11.0 involves improper handling of IP address checks for rate-limiting on the /login and /register routes.

Attackers could bypass the rate-limiting mechanism by spoofing IP addresses. HedgeDoc instances checked for the CloudFlare-specific header 'cf-connecting-ip' and used it instead of the user's real IP address, even when the request did not originate from Cloudflare. This allowed attackers to send multiple login requests or create arbitrary accounts by sending a forged 'cf-connecting-ip' header with each request.

The issue was fixed in version 1.11.0, which ensures proper validation of the source of the 'cf-connecting-ip' header.

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Detection Guidance

Detecting this vulnerability involves checking if your HedgeDoc instance is exposed to IP spoofing via the cf-connecting-ip header. Since the vulnerability allows attackers to bypass rate-limiting by spoofing IP addresses, you can look for signs of unusual activity in your logs.

• Check your HedgeDoc logs for repeated login or registration attempts from the same IP address or multiple cf-connecting-ip headers in a short time frame. This may indicate an attempt to exploit the vulnerability.
• Verify if your HedgeDoc instance is running a version prior to 1.11.0. You can do this by checking the version in the application's settings or by inspecting the source code if you have access.
• Inspect incoming HTTP requests to your HedgeDoc instance for the presence of the cf-connecting-ip header, especially if the requests do not originate from Cloudflare. This can be done using network monitoring tools or by analyzing web server logs.

Example commands to check for suspicious activity in logs (adjust based on your logging setup):

• grep 'cf-connecting-ip' /var/log/hedgedoc/access.log | awk '{print $1}' | sort | uniq -c | sort -nr (to count occurrences of the cf-connecting-ip header)
• grep '/login' /var/log/hedgedoc/access.log | awk '{print $1}' | sort | uniq -c | sort -nr (to count login attempts by IP)
• grep '/register' /var/log/hedgedoc/access.log | awk '{print $1}' | sort | uniq -c | sort -nr (to count registration attempts by IP)

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Impact Analysis

If you are using an affected version of HedgeDoc (prior to 1.11.0), this vulnerability could have several impacts:

• Attackers could spam your HedgeDoc instance with repeated login attempts, potentially leading to brute-force attacks to guess user credentials.
• Attackers could create multiple arbitrary accounts on your instance, which might be used for malicious purposes such as spamming, phishing, or other abusive activities.
• The excessive requests could degrade the performance of your HedgeDoc instance, leading to slower response times or service disruptions for legitimate users.

If your instance is exposed to the internet, the risk of exploitation increases, as attackers can target it remotely without authentication.

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Compliance Impact

This vulnerability could impact compliance with common standards and regulations in the following ways:

• GDPR (General Data Protection Regulation): If attackers exploit this vulnerability to create unauthorized accounts or access user data, it could lead to unauthorized processing or exposure of personal data. This may violate GDPR principles such as data protection by design and default (Article 25) and security of processing (Article 32).
• HIPAA (Health Insurance Portability and Accountability Act): If HedgeDoc is used to store or process protected health information (PHI) and attackers exploit this vulnerability to gain unauthorized access, it could result in a breach of PHI. This would violate HIPAA's Security Rule, which requires safeguards to protect the confidentiality, integrity, and availability of PHI.
• Other standards: The vulnerability could also affect compliance with frameworks like ISO 27001, which requires organizations to implement controls to manage information security risks. Failure to address such vulnerabilities could result in non-compliance with risk management and access control requirements.

Organizations should assess whether this vulnerability could lead to unauthorized access or data breaches and take corrective actions, such as upgrading to the fixed version, to maintain compliance.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Upgrade your HedgeDoc instance to version 1.11.0 or later, as this version includes the fix for the IP spoofing issue.
• If upgrading is not immediately possible, restrict access to the /login and /register routes to trusted IP addresses or networks using firewall rules or web server configurations.
• Disable or modify the handling of the cf-connecting-ip header in your HedgeDoc configuration if your instance is not behind Cloudflare. Ensure that the header is only trusted when requests originate from Cloudflare's IP ranges.
• Monitor your logs for suspicious activity, such as repeated login or registration attempts, and block IP addresses exhibiting such behavior.
• Consider implementing additional rate-limiting measures at the web server or application level to prevent abuse of the login and registration endpoints.

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