CVE-2026-85695
FastChat Unauthenticated Worker Registration SSRF and Model Spoofing
- State
- Published
- Severity
- 9.3 Critical
- Published
- Sep 4, 2026
- Updated
- Oct 1, 2026
- Reserved
- Sep 4, 2026
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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 4.0 | 9.3 Critical | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N | VulnCheck |
| 3.1 | 9.4 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L | VulnCheck |
Weaknesses
- CWE-306 Missing Authentication for Critical Function
Affected Products
| Product | Versions |
|---|---|
FastChatlm-sys |
|
References
- GitHub Issue #3886issue-tracking
- https://github.com/lm-sys/FastChatproduct
- https://github.com/lm-sys/FastChat/blob/v0.2.36/fastchat/serve/controller.pytechnical-description
- VulnCheck Advisory: FastChat Unauthenticated Worker Registration SSRF and Model Spoofingthird-party-advisory
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