CVE-2026-85695
FastChat Unauthenticated Worker Registration SSRF and Model Spoofing
CVSS Score
9.4
EPSS Score
0.0%
EPSS Percentile
0th
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.
| CWE | CWE-306 |
| Vendor | lm-sys |
| Product | fastchat |
| Published | Sep 4, 2026 |
| Last Updated | Sep 4, 2026 |
Stay Ahead of the Next One
Get instant alerts for lm-sys fastchat
Be the first to know when new critical vulnerabilities affecting lm-sys fastchat are published — delivered to Slack, Telegram or Discord.
Get Free Alerts →
Free · No credit card · 60 sec setup
CVSS v3 Breakdown
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
Low
Affected Versions
lm-sys / FastChat
0 ≤ 0.2.36
References
github.com: https://github.com/lm-sys/FastChat/issues/3886 github.com: https://github.com/lm-sys/FastChat github.com: https://github.com/lm-sys/FastChat/blob/v0.2.36/fastchat/serve/controller.py vulncheck.com: https://www.vulncheck.com/advisories/fastchat-unauthenticated-worker-registration-ssrf-and-model-spoofing
Credits
George Chen