CVE-2026-85695
Critical
Description
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.
SeverityCritical
CVSS9.4
Exploit probability—
ProductFastChat
PublishedSep 4, 2026
First seenSep 4, 2026
Weakness typeCWE-306Missing authentication for critical function
How to fix
Sources list no fixed version or patch link for this vulnerability.
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| lm-sys FastChat | v ≤ 0.2.36 | — |
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