What’s Vulnerable › Vulnerabilities

CVE-2026-85695: FastChat Unauthenticated Worker Registration SSRF and Model Spoofing

• Severity: critical (CVSS 9.4 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-04 · updated 2026-09-10
• Weakness: CWE-306

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.

Affected products

• lm-sys/fastchat: through 0.2.36

References

• https://github.com/lm-sys/FastChat
• https://github.com/lm-sys/FastChat/blob/v0.2.36/fastchat/serve/controller.py
• https://github.com/lm-sys/FastChat/issues/3886
• https://www.vulncheck.com/advisories/fastchat-unauthenticated-worker-registration-ssrf-and-model-spoofing

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