nostr:npub18994crjwnldrukwym5lz3y2nae84s84v20m2rkngtjnyg549lr6qvxmd6m question, how TF do I prevent SSRF without setting up an outbound proxy server? Doing DNS lookup I assume will destroy performance, and caching the lookup makes it vulnerable to timing attacks. The internet is broken
Discussion
nostr:npub108pv4cg5ag52nq082kd5leu9ffrn2gdg6g4xdwatn73y36uzplmq9uyev6 like you mentioned, resolving DNS and inspecting the records is the only full-proof way. You’d want to disable the aws/gcp metadata endpoints, 127.0.0.1/localhost, and maybe even all RFC1918 addresses.
The cheating way is to not do any of that and allow arbitrary GETs, BUT fix the issue elsewhere. Disable metadata api (and put a check at program startup), don’t run unauthenticated local services, make the result blind (so the ssrf can’t be used as an intranet port scanner)
ChatGPT generated this response:
Preventing Server-Side Request Forgery (SSRF) without setting up an outbound proxy server requires a combination of security measures and best practices to mitigate the risks associated with this vulnerability. While using an outbound proxy is a recommended approach, there are alternative methods you can employ to enhance your security posture:
Input Validation and Whitelisting:
Sanitize and validate all user-controlled input, especially URLs and parameters that are used in requests. Implement input validation and whitelisting to only allow specific, trusted domains or IP addresses to be used in requests.
URL Parsing and Validation:
Utilize libraries and built-in functions for parsing URLs to ensure they adhere to the expected format. Check the scheme (http/https) and domain of the URL to ensure they are valid and match expectations.
IP Filtering:
Maintain a whitelist of allowed IP addresses or IP address ranges that your application can make requests to. Use firewall rules or network-level controls to enforce IP filtering.
DNS Resolution Security:
Implement proper DNS security measures to prevent attackers from manipulating DNS records to point to malicious destinations. Consider using DNS filtering services to block access to known malicious domains.
Use of Request Libraries:
If your application uses libraries or frameworks to make HTTP requests, ensure that these libraries are configured securely. Check if the libraries have options to restrict access to internal resources and provide necessary configurations.
HTTP Redirects and Shortened URLs:
Be cautious of HTTP redirects, as they can be abused to redirect requests to internal resources. Avoid using shortened URLs, as they can obscure the actual destination.
Network Segmentation:
If possible, isolate the components of your application’s infrastructure so that sensitive resources are not directly accessible from external systems.
Server Configuration:
Configure your server to reject or block requests to private or internal IP addresses. Disable or restrict protocols like file, gopher, or other potentially dangerous protocols.
Authentication and Authorization:
Implement strong authentication and authorization mechanisms to control access to sensitive resources within your application. Security Testing and Auditing:
Regularly conduct security testing, including penetration testing and code reviews, to identify and address potential vulnerabilities. Stay informed about the latest SSRF attack techniques and security best practices.
It’s important to note that while these measures can help mitigate SSRF risks, they may not provide the same level of security as setting up an outbound proxy server. Outbound proxies offer a centralized point for managing and monitoring outgoing requests, making them a more comprehensive solution for preventing SSRF attacks. If possible, consider the advantages of using an outbound proxy server in your security strategy.
