Fastgpt EUVD-2026-21507

CVSS 5.3 with vector AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N indicates a network-accessible, unauthenticated attack with low complexity and confidentiality impact. The CVSS reflects that this is information disclosure rather than code execution or service disruption. However, real-world risk is elevated by several factors: (1) the vulnerability is enabled by default due to a permissive configuration, (2) no authentication is required, (3) attack complexity is low-simple URL manipulation in an endpoint accessible to anyone, (4) SSRF is a high-value primitive that often precedes further attacks such as credential theft from cloud metadata endpoints, lateral movement to internal services, or amplification for amplified DDoS attacks. The moderate CVSS score underestimates practical impact in environments with sensitive internal services. No public exploit code or CISA KEV status was reported at analysis time, but the vulnerability is trivial to weaponize given the public advisory. Organizations running FastGPT in networks with unprotected internal resources face material risk of reconnaissance and data exfiltration.

An unauthenticated attacker discovers or enumerates a FastGPT instance on the internet and sends a POST request to /api/core/app/mcpTools/runTool with a URL parameter pointing to an internal service, such as http://localhost:5432 (PostgreSQL), http://192.168.1.100:6379 (Redis), or http://169.254.169.254/latest/meta-data/ (AWS metadata endpoint). Because CHECK_INTERNAL_IP is not enabled by default and no authentication is required, the FastGPT server processes the request and attempts to establish a connection to the attacker-specified URL. The response-which may include error messages, service banners, or metadata-is returned to the attacker, allowing reconnaissance of internal infrastructure and extraction of credentials or configuration data. No public exploit code was identified at the time of analysis, but exploitation requires only basic HTTP knowledge and is trivial to implement.