FastChat Unauthenticated Worker Registration SSRF and Model Spoofing

{
  "id": "34ae50bdc2764546de3a0d63190b27a7a2559e3bae412793145ffd878f75c93f",
  "url": "https://osv.dev/vulnerability/CVE-2026-85695",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "FastChat Unauthenticated Worker Registration SSRF and Model Spoofing",
    "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.",
    "evidence": "osv:CVE-2026-85695",
    "products": [],
    "severity": "critical",
    "structured": {
      "id": "CVE-2026-85695",
      "aliases": [
        "CVE-2026-85695"
      ],
      "metrics": [
        {
          "type": "CVSS_V4",
          "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"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/lm-sys/fastchat",
              "type": "GIT",
              "events": [
                {
                  "introduced": "0"
                },
                {
                  "last_affected": "b21d0f780ca4472a13714262a0790f2ee1ade659"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "last_affected": "0.2.36"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StandardRange"
                  }
                ]
              }
            }
          ],
          "versions": [
            "v0.2.36",
            "v0.2.35",
            "v0.2.34",
            "v0.2.33",
            "v0.2.32",
            "v0.2.31",
            "v0.2.30",
            "v0.2.29",
            "v0.2.28",
            "v0.2.27",
            "v0.2.26",
            "v0.2.25",
            "v0.2.23",
            "v0.2.22",
            "v0.2.21",
            "v0.2.18",
            "v0.2.14",
            "v0.2.9",
            "v0.2.5",
            "v0.2.3",
            "v0.2.1",
            "v0.1.10"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-85695.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:28.210405354Z",
      "provider": "osv",
      "references": [
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/85xxx/CVE-2026-85695.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-85695",
        "https://www.vulncheck.com/advisories/fastchat-unauthenticated-worker-registration-ssrf-and-model-spoofing",
        "https://github.com/lm-sys/FastChat/issues/3886",
        "https://github.com/lm-sys/FastChat",
        "https://github.com/lm-sys/FastChat/blob/v0.2.36/fastchat/serve/controller.py"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-306"
        ],
        "cna_assigner": "VulnCheck",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/85xxx/CVE-2026-85695.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-85695",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 494827,
  "published_at": "2026-09-04T14:32:38.104+00:00"
}