FastGPT's isInternalAddress() function resolves hostnames using dns.resolve4() and dns.resolve6() to verify if the IP addresses belong to private ranges. However, the actual HTTP request uses a separate DNS resolution, creating a window where the DNS record can change between the check and the request. This TOCTOU race condition allows DNS rebinding attacks that can circumvent internal address validation. The vulnerability affects FastGPT versions up to 4.14.11. There is no vendor advisory or patch available yet.

Successful exploitation of this vulnerability could allow an attacker to bypass internal address checks by manipulating DNS responses between the validation and the actual HTTP request. This could lead to unauthorized access to internal network resources or services that are intended to be protected by the internal address validation. The CVSS score of 6.3 reflects a medium severity with high confidentiality impact but no impact on integrity or availability.

Patch status is not yet confirmed — check the vendor advisory for current remediation guidance. Until a fix is available, users should consider mitigating DNS rebinding risks by implementing network-level protections such as DNS filtering or restricting DNS responses, and reviewing internal address validation logic to avoid separate DNS resolutions between check and use. Monitor vendor channels for updates and official patches.