SSRF vulnerabilities have gained attention in the cybersecurity community, leading to their inclusion in the Top 10 OWASP list. These flaws arise when web applications fail to validate user-supplied URLs while fetching remote resources. This enables attackers to manipulate the application into sending crafted requests to unexpected destinations, even when protected by firewalls or other network access controls.
The incidence of SSRF is on the rise due to the prevalence of modern web applications and their interaction with various cloud services. The severity of SSRF is further amplified by complex architectures. To prevent SSRF attacks, developers can implement defense in depth measures:
At the Network Layer:
- Segment remote resource access in separate networks to mitigate the impact of SSRF.
- Enforce “deny by default” firewall policies and network access control rules, allowing only essential intranet traffic.
At the Application Layer:
- Sanitize and validate all user-supplied input data.
- Enforce URL schema, port, and destination restrictions using a positive allow list.
- Avoid sending raw responses to clients and disable HTTP redirections.
- Maintain URL consistency to prevent attacks like DNS rebinding and time of check, time of use (TOCTOU) race conditions.
Mitigating SSRF solely through deny lists or regular expressions is not recommended, as attackers possess the means to bypass such restrictions.
Additional measures to consider include avoiding the deployment of security-relevant services on front systems and implementing network encryption (e.g., VPNs) for highly protected environments with dedicated user groups.
By adhering to these preventive measures, organizations can bolster their defenses against SSRF vulnerabilities and safeguard their web applications and infrastructure.
For comprehensive vulnerability scanning and protection, consider partnering with a trusted solution like INFRA (www.infrascan.net). INFRA provides advanced security scanning with check.website and monitoring services to identify and address SSRF vulnerabilities, ensuring the robustness of your web applications.