Advanced Techniques for Exploiting SSRF Vulnerabilities

Server-Side Request Forgery (SSRF) is a powerful vulnerability that allows attackers to manipulate a server into making unauthorized requests to internal or external resources. By exploiting user-controlled inputs that the server uses to make network requests, attackers can access sensitive information or perform unintended actions on internal services.

SSRF vulnerabilities occur when a server processes user-controlled inputs, like URLs or IP addresses, to interact with resources. If the server fails to validate these inputs, attackers can target internal or sensitive endpoints.

Key Concepts:

Server-Side Requests: Servers make requests based on user input, potentially accessing internal resources.Unrestricted Requests: Without proper restrictions, these requests can expose internal services or data.

Types of SSRF Attacks

Internal Network Access: SSRF can be used to probe and access internal services, such as APIs or databases, that aren’t exposed externally.Cloud Metadata Service Exploitation: Attackers can access cloud metadata services, revealing instance details, credentials, and configuration data.Port Scanning: SSRF enables internal port scanning, allowing attackers to map out internal services and identify vulnerabilities.

Conducting an SSRF Attack

Reconnaissance and Discovery:Identify SSRF Entry Points: Look for input fields or parameters accepting URLs or IP addresses. Common parameters include callback_url, image_url, or api_endpoint.Analyze Traffic: Use tools like Burp Suite or OWASP ZAP to inspect network traffic and identify endpoints that utilize user input for requests. Crawling the site can also reveal hidden parameters.

2. Payload Crafting:

Craft payloads to exploit SSRF vulnerabilities. Common examples include:

http://localhost/

http://127.0.0.1/

http://internal-service/

Target cloud metadata services with payloads like:

AWS: http://169.254.169.254/latest/meta-data/

Azure: http://169.254.169.254/metadata/instance?api-version=2019-08-15

These can retrieve instance details or credentials. Additionally, test access to internal files or services using protocols like ftp://127.0.0.1/, file:///etc/passwd, or gopher://127.0.0.1/.

3. Testing and Exploitation:

Submit crafted payloads using Burp Suite’s Intruder or custom scripts.Look for responses that indicate successful exploitation, such as internal service information. Analyze responses for sensitive data, error messages, or unexpected behavior that could reveal internal details.

4. Exploitation and Information Extraction:

Extract credentials or configuration data by targeting cloud metadata endpoints.Retrieve sensitive server files using payloads like file:///etc/passwd.Use SSRF to map internal services and ports, revealing additional targets for further exploitation.