SSRF

SSRF, or server-side request forgery, is a type of vulnerability in which a server is tricked into making requests to unintended destinations, often using user-controlled input to select the target URL or resource. The server acts as a proxy, fetching data on behalf of a client, which can reveal internal services or expose sensitive resources.

Common vectors involve applications that fetch remote content, proxy user-supplied URLs, or load images or resources based on parameters. If the server can reach internal networks, cloud metadata endpoints, or other protected services, an attacker may access those resources or exfiltrate data. SSRF can enable enumeration of internal hosts, access to private storage, or interaction with services that are not normally reachable from the public internet.

Impact ranges from information disclosure to substantial breach of internal networks, depending on the architecture and access controls. In cloud environments, SSRF can be used to access instance metadata or services that return credentials or tokens. In some configurations, SSRF could lead to further exploitation such as reaching other services, performing unauthorized actions, or causing denial of service.

Mitigation strategies include tightening input handling with allowlists of permitted destinations, validating and canonicalizing URLs, and blocking or isolating access to internal resources and metadata services. Network controls such as egress filtering, restricted service accounts, and separate trusted zones help limit exposure. Implementing timeouts, using dedicated server components to mediate external requests, and comprehensive logging and monitoring are also recommended to detect and prevent SSRF attempts.

Security testing should verify that user-controllable destinations cannot reach restricted endpoints, and that defenses such as allowlists and network restrictions are effective. Ongoing review of dependencies and deployment environments is advised.