CVE-2026-85695: FastChat Unauthenticated Worker Registration SSRF and Model Spoofing
FastChat contains an authentication bypass vulnerability in the /registerworker endpoint that allows unauthenticated attackers to register arbitrary worker addresses and perform server-side request forgery. Attackers can register malicious workers under victim model names to intercept user prompts, images, and responses, or probe internal network ports across the worker mesh.
Affected Software
Event History
Frequently Asked Questions
Which FastChat deployments are exposed?
Deployments whose /register_worker endpoint is reachable by an unauthenticated attacker are exposed. The issue allows arbitrary worker addresses to be registered with the controller.
What can an attacker do after registering a malicious worker?
An attacker can register a worker under a victim model name and intercept user prompts, images, and responses routed to that model. They can also use registered worker addresses to induce server-side requests and probe internal network ports across the worker mesh.
Does exploitation require credentials or user interaction?
No. The provided severity vector identifies the issue as network-accessible with low attack complexity, no privileges required, and no user interaction required.