Vulnerability-Lookup

GHSA-46FR-7J3V-277V

Vulnerability from github – Published: 2026-09-04 15:36 – Updated: 2026-09-04 15:36

Details

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.

Severity

9.4 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

9.3 (Critical)


                  
                    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

Show details on source website

JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-85695"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-306"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-09-04T15:17:47Z",
    "severity": "CRITICAL"
  },
  "details": "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.",
  "id": "GHSA-46fr-7j3v-277v",
  "modified": "2026-09-04T15:36:16Z",
  "published": "2026-09-04T15:36:16Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-85695"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lm-sys/FastChat/issues/3886"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lm-sys/FastChat"
    },
    {
      "type": "WEB",
      "url": "https://github.com/lm-sys/FastChat/blob/v0.2.36/fastchat/serve/controller.py"
    },
    {
      "type": "WEB",
      "url": "https://www.vulncheck.com/advisories/fastchat-unauthenticated-worker-registration-ssrf-and-model-spoofing"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L",
      "type": "CVSS_V3"
    },
    {
      "score": "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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-85695 (GCVE-0-2026-85695)

Vulnerability from cvelistv5 – Published: 2026-09-04 14:32 – Updated: 2026-09-04 15:05

Title

FastChat Unauthenticated Worker Registration SSRF and Model Spoofing

Summary

Severity

9.3 (Critical)


                        
                          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

9.4 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L

SSVC

Exploitation: none Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-04 15:04 UTC

CWE

CWE-306 - Missing Authentication for Critical Function

Assigner

VulnCheck mitre root

References

4 references

URL	Tags
https://github.com/lm-sys/FastChat/issues/3886	issue-tracking
https://github.com/lm-sys/FastChat	product
https://github.com/lm-sys/FastChat/blob/v0.2.36/f…	technical-description
https://www.vulncheck.com/advisories/fastchat-una…	third-party-advisory

Impacted products

1 product

Vendor	Product	Version
lm-sys	FastChat	Affected: 0 , ≤ 0.2.36 (semver)

Date Public

2026-06-12 00:00

Credits

George Chen

Show details on NVD website

JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-85695",
                "options": [
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                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "total"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-09-04T15:04:53.369519Z",
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          "defaultStatus": "unaffected",
          "packageURL": "pkg:pypi/fschat",
          "product": "FastChat",
          "vendor": "lm-sys",
          "versions": [
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              "lessThanOrEqual": "0.2.36",
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              "version": "0",
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          "type": "finder",
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      "descriptions": [
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          "lang": "en",
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        }
      ],
      "metrics": [
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          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "NONE",
            "attackVector": "NETWORK",
            "baseScore": 9.3,
            "baseSeverity": "CRITICAL",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
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            "userInteraction": "NONE",
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            "version": "3.1"
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          "tags": [
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          "url": "https://github.com/lm-sys/FastChat/issues/3886"
        },
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          "tags": [
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        },
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          "tags": [
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          ],
          "url": "https://www.vulncheck.com/advisories/fastchat-unauthenticated-worker-registration-ssrf-and-model-spoofing"
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Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

Action not permitted

GHSA-46FR-7J3V-277V

CVE-2026-85695 (GCVE-0-2026-85695)

Tags

Sightings

Nomenclature