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

Quick assessment

Affected
lm-sys FastChat
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

LMSYS FastChat是LMSYS组织开源的一个用于训练、部署和评估基于大型语言模型的聊天机器人的开放平台。 LMSYS FastChat 0.2.36及之前版本存在授权问题漏洞，该漏洞源于/register_worker端点存在身份验证绕过，可能导致未经身份验证的攻击者注册任意worker地址并执行服务端请求伪造，从而拦截用户提示、图像和响应，或探测内部网络端口。

CVSS 9.4 · Critical EPSS 0.41% · P35

Affected Version Matrix 1

VendorProduct Version RangeStatus
lm-sys FastChat ≤ 0.2.36 affected
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I. Basic Information for CVE-2026-85695

Vulnerability Information
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Vulnerability Title
FastChat Unauthenticated Worker Registration SSRF and Model Spoofing
Source: CVE Program / CVE List V5
Vulnerability 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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L
Source: CVE Program / CVE List V5
Vulnerability Type
关键功能的认证机制缺失
Source: CVE Program / CVE List V5
Vulnerability Title
LMSYS FastChat 授权问题漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
LMSYS FastChat是LMSYS组织开源的一个用于训练、部署和评估基于大型语言模型的聊天机器人的开放平台。 LMSYS FastChat 0.2.36及之前版本存在授权问题漏洞，该漏洞源于/register_worker端点存在身份验证绕过，可能导致未经身份验证的攻击者注册任意worker地址并执行服务端请求伪造，从而拦截用户提示、图像和响应，或探测内部网络端口。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
lm-sys FastChat 0 ~ 0.2.36 -

II. Public POCs for CVE-2026-85695

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III. Intelligence Information for CVE-2026-85695

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Vendor Advisories for CVE-2026-85695 (1)

Proof of Concept for CVE-2026-85695 (1)

Security Blog Posts for CVE-2026-85695 (1)

Other References for CVE-2026-85695 (1)

IV. Related Vulnerabilities

Same product: FastChat
Same vendor: lm-sys
Same weakness: CWE-306

V. Comments for CVE-2026-85695

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