{"cve":"CVE-2026-45019","nvd":{"published":"2026-08-25T20:16:55.910","modified":"2026-09-09T21:07:31.353","status":"Deferred","description":"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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","score":7.2},"cwes":["CWE-918"],"references":["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/commit/0565fd0eccb915fce159929598b053ed79f6e0c9","https://github.com/Chainlit/chainlit/releases/tag/2.12.0","https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:50:17.453294893+00:00"},"epss":{"cve":"CVE-2026-45019","score":0.00434,"percentile":0.37751,"date":"2026-10-31"},"kev":null,"osv":[{"id":"GHSA-hvfh-5mj3-5f3j","url":"https://osv.dev/vulnerability/GHSA-hvfh-5mj3-5f3j","summary":"Chainlist has SSRF via MCP SSE and streamable-http transports that allows unauthenticated internal network access","modified":"2026-09-10T12:25:53.170074650Z","packages":[{"ecosystem":"PyPI","name":"chainlit","purl":"pkg:pypi/chainlit","ranges":[">=2.4.0rc0 <2.12.0"],"fixed":["2.12.0"]}]},{"id":"PYSEC-2026-3811","url":"https://osv.dev/vulnerability/PYSEC-2026-3811","summary":"Chainlist has SSRF via MCP SSE and streamable-http transports that allows unauthenticated internal network access","modified":"2026-09-10T12:15:04.072233508Z","packages":[{"ecosystem":"PyPI","name":"chainlit","purl":"pkg:pypi/chainlit","ranges":[">=2.4.0rc0 <2.12.0"],"fixed":["2.12.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}