CVE-2026-85695

FastChat Unauthenticated Worker Registration SSRF and Model Spoofing

Published Sep 4, 2026 CVSS 4.0 · 9.3 Critical EPSS < 1% KEV · Not listed
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.

Remediation

No solution or workaround provided in the CVE record

Tracking

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Advisories

No advisories available
History
Type Values Removed Values Added
First Time appeared Lmsys
Lmsys fastchat
CPEs cpe:2.3:a:lmsys:fastchat:*:*:*:*:*:*:*:*
Vendors & Products Lmsys
Lmsys fastchat
Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'yes', 'Exploitation': 'none', 'Technical Impact': 'total'}, 'version': '2.0.3'}

Type Values Removed Values Added
First Time appeared Lm-sys
Lm-sys fastchat
Vendors & Products Lm-sys
Lm-sys fastchat
Type Values Removed Values Added
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.
Title FastChat Unauthenticated Worker Registration SSRF and Model Spoofing
Weaknesses CWE-306
References
Metrics cvssV3_1

{'score': 9.4, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L'}

cvssV4_0

{'score': 9.3, 'vector': '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'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
VulnCheck
Published
Updated
Oct 1, 2026, 3:21 PM
Reserved
Sep 4, 2026, 1:51 PM
Status
Deferred
Published
Sep 4, 2026, 3:17 PM
Modified
Sep 10, 2026, 3:53 PM