Unauthenticated SSRF and model spoofing via worker registration
Published Sep 4, 2026 · Updated Sep 4, 2026
Authentication bypass in LMSYS FastChat 0 through 0.2.36 allows remote attackers to trigger SSRF and spoof model workers. The controller's /register_worker route accepts an unauthenticated worker_name URL, fetches its /worker_get_status path, and registers the address without validation. Network access to the controller is required; a malicious worker can probe internal ports, receive proxied prompts and images, and supply altered responses.
Summary
What happened
Authentication bypass in LMSYS FastChat 0 through 0.2.36 allows remote attackers to trigger SSRF and spoof model workers. The controller's /register_worker route accepts an unauthenticated worker_name URL, fetches its /worker_get_status path, and registers the address without validation. Network access to the controller is required; a malicious worker can probe internal ports, receive proxied prompts and images, and supply altered responses.
The record
- CVE
- CVE-2026-85695
- Published
- Sep 4, 2026
- Updated
- Sep 4, 2026
- Vendor
- LMSYS Org
- Product
- FastChat
- Classifications
- CWE-306, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 4, 2026CVE publishedPublication date reported by the CVE source.
- Sep 4, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0 <=0.2.36
What conditions does exploitation require?
What is affected?
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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