CVE-2026-85695: Lm-Sys Fastchat

Critical severity, CVSS 9.4. EPSS: 0.7% chance of exploitation in the next 30 days.

FastChat contains an authentication bypass vulnerability in the /register_worker 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 products

• Lm-Sys Fastchat: up to and including 0.2.36

Published 2026-09-04. Last modified 2026-09-10.