SSRF Vectors
Web applications often act as intermediaries between clients and internal services, making them potential entry points for SSRF attacks. Attackers exploit misconfigured server-side redirects and network traversal techniques to bypass security boundaries, accessing internal systems, APIs, or sensitive data. This section explores common SSRF attack vectors and how they leverage these mechanisms to compromise networked environments.
Internal Service Access via Misconfigured Redirects¶
Many applications use redirects to forward users to internal resources (e.g., APIs, authentication endpoints). If these redirects are not properly validated, attackers can manipulate them to access internal services. For example, a form submission might be directed to an internal API endpoint, allowing an attacker to intercept or modify the request.
Example: A vulnerable login form redirects to an internal authentication service (http://localhost:8080/auth). An attacker could exploit this by crafting a request that bypasses validation and accesses the internal service.
This request could expose credentials, internal APIs, or other sensitive data if the server does not validate the uri parameter.
Network Traversal Using Protocols¶
SSRF attacks often leverage protocols like HTTP, FTP, or even less common ones like Gopher or LDAP to traverse internal networks. Attackers may use these protocols to access internal IP addresses or services that are not exposed to the public internet.
Example: A server configured to accept HTTP requests might be tricked into accessing an internal database server via a crafted URL.
If the server allows such requests, the attacker could retrieve database credentials or execute arbitrary commands, depending on the service's configuration.
DNS Rebinding Exploits¶
DNS rebinding is a technique where an attacker tricks a server into resolving a domain to an internal IP address after an initial resolution to a public IP. This can bypass CORS or firewall restrictions, allowing the server to access internal resources.
Example: An attacker registers a domain (attacker.com) that resolves to their IP first, then to an internal server (10.0.0.5) after a short timeout. The server, unaware of the change, may make requests to the internal IP.
This could lead to unauthorized access to internal services, such as internal APIs or file storage systems.
Proxy Configuration Exploitation¶
If a server is configured to use a proxy (e.g., for load balancing or caching), an attacker might exploit this to route traffic through the proxy to internal services. This is particularly effective if the proxy is misconfigured to allow unauthenticated access.
Example: A server using a proxy (http://proxy:8080) could be manipulated to forward requests to an internal service.
This could expose internal services to the attacker, depending on the proxy's configuration and the server's trust relationships.
Key takeaways¶
- SSRF exploits misconfigurations to access internal services via redirects or network traversal.
- Attackers use protocols like HTTP, FTP, or DNS rebinding to bypass security boundaries.
- Network traversal techniques can expose sensitive data or services within the internal network.
- Always validate and sanitize user-provided input, especially when handling URLs or redirects.
- Implement strict network segmentation and restrict internal service access to trusted sources.