Chainlit: SSRF via MCP SSE and streamable-http transports allows unauthenticated internal network access

{
  "id": "fa62b5834fdbab53765aed525d0f1268aeed04c72f6b6aeb4e4afa6bcaa7d9eb",
  "url": "https://osv.dev/vulnerability/CVE-2026-45019",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "Chainlit: SSRF via MCP SSE and streamable-http transports allows unauthenticated internal network access",
    "summary": "Chainlit is a Python framework for building production-ready conversational AI applications. From 2.4.0rc0 until 2.12.0, Chainlit deployments with features.mcp.enabled set to true in .chainlit/config.toml expose the POST /mcp endpoint without requiring authentication. For sse and streamable-http transports, ConnectSseMCPRequest and ConnectStreamableHttpMCPRequest in backend/chainlit/types.py accept a user-controlled url and optional headers dictionary without scheme validation, private-address filtering, or an allowlist. The connect_mcp handler in backend/chainlit/server.py passes these values to sse_client() or streamablehttp_client(), allowing the Chainlit server to make blind outbound requests to arbitrary internal or external services, including cloud metadata endpoints, with attacker-controlled Authorization and Cookie headers. The SSE URL sink has existed since 2.4.0rc0, while attacker-controlled header forwarding and streamable-http support were added in 2.6.4. The response is consumed internally and not returned, but the attacker can issue state-changing authenticated requests, discover internal services, scan ports, and probe metadata endpoints. This issue is fixed in version 2.12.0.",
    "evidence": "osv:CVE-2026-45019",
    "products": [],
    "severity": "high",
    "structured": {
      "id": "CVE-2026-45019",
      "aliases": [
        "CVE-2026-45019",
        "GHSA-hvfh-5mj3-5f3j",
        "PYSEC-2026-3811"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N"
        }
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://github.com/chainlit/chainlit",
              "type": "GIT",
              "events": [
                {
                  "introduced": "dc13fc0c858ce65814b685ee39dc112a3bd38c87"
                },
                {
                  "fixed": "0565fd0eccb915fce159929598b053ed79f6e0c9"
                }
              ],
              "database_specific": {
                "extracted_events": [
                  {
                    "range": [
                      {
                        "introduced": "2.4.0rc0"
                      },
                      {
                        "fixed": "2.12.0"
                      }
                    ],
                    "source": "AFFECTED_FIELD",
                    "strategy": "StringRangeExpression"
                  },
                  {
                    "range": [
                      {
                        "fixed": "0565fd0eccb915fce159929598b053ed79f6e0c9"
                      }
                    ],
                    "source": "REFERENCES_COMMIT"
                  },
                  {
                    "range": [
                      {
                        "fixed": "0565fd0eccb915fce159929598b053ed79f6e0c9"
                      }
                    ],
                    "source": "REFERENCES_TAG",
                    "original_tag": "2.12.0"
                  },
                  {
                    "range": [
                      {
                        "introduced": "0"
                      },
                      {
                        "fixed": "2.12.0"
                      }
                    ],
                    "source": "DESCRIPTION"
                  }
                ]
              }
            }
          ],
          "versions": [
            "2.11.1",
            "2.11.0",
            "2.10.1",
            "2.10.0",
            "2.9.6",
            "2.9.5",
            "2.9.4",
            "2.9.3",
            "2.9.2",
            "2.9.1",
            "2.9.0",
            "2.8.5",
            "2.8.4",
            "2.8.3",
            "2.8.2",
            "2.8.1",
            "2.8.0",
            "2.7.2",
            "2.7.1.1",
            "2.7.1",
            "2.7.0",
            "2.6.9",
            "2.6.8",
            "2.6.7",
            "2.6.6",
            "2.6.5",
            "2.6.4",
            "2.6.3",
            "2.6.2",
            "2.6.1",
            "2.6.0",
            "2.5.5",
            "2.4.400",
            "2.4.302",
            "2.4.301",
            "2.4.3",
            "2.4.201",
            "2.4.2",
            "2.4.1",
            "2.4.0",
            "2.4.0rc0"
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-45019.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:35.865165407Z",
      "provider": "osv",
      "references": [
        "https://github.com/Chainlit/chainlit/releases/tag/2.12.0",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45019.json",
        "https://github.com/Chainlit/chainlit/blob/2.12.0/docs/security-advisory-2026-mcp.md#spl-2026-002--ssrf-via-mcp-streamable-http--sse",
        "https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-45019",
        "https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9"
      ],
      "provider_metadata": {
        "cwe_ids": [
          "CWE-918"
        ],
        "cna_assigner": "GitHub_M",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45019.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-45019",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 503365,
  "published_at": "2026-08-25T19:20:59.339+00:00"
}