SSRF: The Overlooked Vulnerability in Modern Web Apps
By HackTool Team
Server-side request forgery happens when an attacker can make your server send HTTP requests to destinations they choose. It sounds niche, but SSRF was the root cause of the 2019 Capital One breach that exposed 100 million records.
How SSRF Works
Any feature where your application fetches a URL on behalf of the user is a potential SSRF vector:
The attacker provides a URL pointing to an internal service — like the cloud metadata endpoint at 169.254.169.254 — and your server dutifully fetches it.
Why It Matters
In cloud environments, the metadata endpoint returns IAM credentials, instance configuration, and sometimes database connection strings. An SSRF vulnerability can turn a simple URL parameter into full cloud account compromise.
Even without cloud metadata, SSRF gives attackers access to internal services behind the firewall: admin panels, databases, message queues, and monitoring tools that are assumed to be unreachable from the internet.
Common Bypass Techniques
Simple URL validation is easy to bypass:
Detection
SSRF detection involves sending payloads that attempt to reach a canary service. The scanner provides a callback URL and checks whether the target server makes a request to it. If the target fetches the canary, the SSRF is confirmed.
For blind SSRF where there is no visible response difference, out-of-band detection using DNS callbacks is more reliable than response-based analysis.