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TI-2026-58806 Aliases CVE-2026-85695GHSA-46fr-7j3v-277v

FastChat Unauthenticated Worker Registration SSRF and Model Spoofing

Priority MEDIUM 49CWE-306Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Attack requirements
None
Impact type
Security bypass
Confidentiality · integrity · availability
High · High · Low
Fix status
No fix listed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-306.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.0072 54th percentileScored 2026-11-07
Fix No fix listed No fixed version in the sources yet

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
Yes
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
lm-sysFastChatup to 0.2.36—No fix listedCNA
  • FastChat Vendorlm-sys Affected up to 0.2.36 Fixed in — No fix listed CNA

Remediation

No fixed version listed by the sources yet.

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-85695
  2. 2026-10-03 Alias added: GHSA-46fr-7j3v-277v

References

Other 3

  • TI-2024-09320 SSRF in POST /worker_generate_stream API endpoint in lm-sys/fastchat CVSS 3.0CRITICAL 9.3
  • TI-2024-11482 Server Side Request Forgery in lm-sys/fastchat CVSS 3.0HIGH 7.5
  • TI-2024-10750 Server-Side Request Forgery in lm-sys/fastchat CVSS 3.0HIGH 7.5
  • TI-2024-10115 Denial of Service in lm-sys/fastchat CVSS 3.0HIGH 7.5
  • TI-2024-10111 Denial of Service (DoS) via Multipart Boundary in lm-sys/fastchat CVSS 3.0HIGH 7.5
  • TI-2026-05795 lm-sys fastchat Arena Side-by-Side View add_text control flow CVSS 4.0MEDIUM 6.9
See all 9 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences