CVE-2025-32013

Remediation/Mitigation Strategy for CVE-2025-32013 in LNbits

Vulnerability Description:

Server-Side Request Forgery (SSRF) in LNbits’ LNURL authentication handling. The application uses a user-provided callback URL to make HTTP requests using the httpx library with redirect following enabled. Insufficient validation of the callback URL allows attackers to specify internal network addresses.

Severity:

Critical (CVSS v3.1 Score: 9.3)

Known Exploit:

An attacker can exploit this vulnerability by crafting a malicious LNURL authentication request containing a callback URL pointing to an internal resource, such as:

  • Internal services (e.g., databases, management interfaces)
  • Internal network devices
  • Cloud provider metadata endpoints

By doing so, the attacker can:

  • Gather sensitive information from internal resources.
  • Potentially execute commands on internal systems (depending on the nature of the accessed resource).
  • Bypass network firewalls and security controls.

Remediation:

  1. Input Validation: Implement strict input validation on the callback URL parameter used in the LNURL authentication process. This should include:

    • URL Scheme Whitelisting: Only allow specific, approved URL schemes (e.g., https). Reject http, file, ftp, and other potentially dangerous schemes.
    • Domain Whitelisting/Blacklisting: Implement a whitelist of allowed domains or a blacklist of known malicious or private IP address ranges. Consider using a regularly updated list of private IP address ranges and reserved domain names.
    • IP Address Validation: Explicitly reject callback URLs that resolve to private IP addresses (e.g., 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 127.0.0.1/8) or localhost. Use socket.gethostbyname() or similar functionality to resolve the hostname and validate the resulting IP address.
    • Regular Expression Filtering: Implement a robust regular expression to enforce a valid URL format and prevent URL encoding exploits (e.g., using URL encoded characters for IP addresses).
    • Length Limitation: Enforce a reasonable maximum length for the callback URL to prevent buffer overflow or other related issues.

  2. Disable Redirect Following (If Possible): If the functionality doesn’t strictly require it, disable redirect following in the httpx library. This will prevent the application from automatically following redirects to internal addresses. If redirect following is necessary, ensure that each redirect target is subject to the same validation checks.

  3. Implement a Proxy Server (Recommended): Route all outbound HTTP requests for LNURL callbacks through a secure proxy server. Configure the proxy server with strict access control policies to prevent access to internal resources. This adds an additional layer of security and helps to centralize outbound traffic monitoring.

  4. Rate Limiting: Implement rate limiting on LNURL authentication requests to prevent attackers from rapidly exploiting the vulnerability.

Mitigation:

  1. Network Segmentation: Segment the LNbits server from internal resources using network firewalls and access control lists. This will limit the impact of a successful SSRF attack.

  2. Least Privilege Principle: Ensure that the LNbits application runs with the minimum required privileges. Avoid granting the application unnecessary access to internal resources.

  3. Monitoring and Alerting: Implement monitoring and alerting for suspicious outbound HTTP requests originating from the LNbits server. Look for requests to internal IP addresses, unusual ports, or unexpected domains.

  4. Regular Security Audits: Conduct regular security audits and penetration testing to identify and address potential vulnerabilities in the LNbits application and its infrastructure.

  5. Update Dependencies: Ensure that all dependencies, including the httpx library, are up to date with the latest security patches.

Implementation Priority:

High - Implement the remediation strategies immediately. The severity of the vulnerability warrants urgent action.

Assigner

Date

  • Published Date: 2025-04-06 20:15:15
  • Updated Date: 2025-04-06 20:15:15

More Details

CVE-2025-32013