{"id":"CVE-2026-45019","summary":"Chainlit: SSRF via MCP SSE and streamable-http transports allows unauthenticated internal network access","details":"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.","aliases":["GHSA-hvfh-5mj3-5f3j"],"modified":"2026-08-29T03:46:13.917274011Z","published":"2026-08-25T19:20:59.339Z","database_specific":{"cna_assigner":"GitHub_M","cwe_ids":["CWE-918"],"osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45019.json"},"references":[{"type":"WEB","url":"https://github.com/Chainlit/chainlit/releases/tag/2.12.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/45xxx/CVE-2026-45019.json"},{"type":"ADVISORY","url":"https://github.com/Chainlit/chainlit/blob/2.12.0/docs/security-advisory-2026-mcp.md#spl-2026-002--ssrf-via-mcp-streamable-http--sse"},{"type":"ADVISORY","url":"https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45019"},{"type":"FIX","url":"https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://github.com/chainlit/chainlit","events":[{"introduced":"dc13fc0c858ce65814b685ee39dc112a3bd38c87"},{"fixed":"0565fd0eccb915fce159929598b053ed79f6e0c9"}],"database_specific":{"source":["AFFECTED_FIELD","REFERENCES"],"extracted_events":[{"introduced":"2.4.0rc0"},{"fixed":"2.12.0"}]}}],"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"}}],"schema_version":"1.9.0","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N"}]}