{"id":"CVE-2026-45019","title":"Chainlit is a Python framework for building production-ready conversational AI applications","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 wi…","severity":"high","cvss":7.2,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N","cwe":["CWE-918"],"vendor":"chainlit","product":"chainlit","affected":["chainlit >= 2.4.0rc0, <= 2.11.1"],"patched":["chainlit 2.12.0"],"published":"2026-08-25","updated":"2026-09-09","sourceUpdated":"2026-09-09T21:07:31.353","source":"NVD","sourceUrl":"https://nvd.nist.gov/vuln/detail/CVE-2026-45019","references":[{"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","label":"security-advisories@github.com"},{"url":"https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9","label":"security-advisories@github.com"},{"url":"https://github.com/Chainlit/chainlit/releases/tag/2.12.0","label":"security-advisories@github.com"},{"url":"https://github.com/Chainlit/chainlit/security/advisories/GHSA-hvfh-5mj3-5f3j","label":"security-advisories@github.com"},{"url":"https://github.com/advisories/GHSA-hvfh-5mj3-5f3j"},{"url":"https://github.com/Chainlit/chainlit"},{"url":"https://pypi.org/project/chainlit"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2026-45019"}],"tags":["nvd","ghsa","pip","osv"],"epss":0.00319,"epssPercentile":0.25043,"aliases":["GHSA-hvfh-5mj3-5f3j","PYSEC-2026-3811"],"ecosystem":"pip","ingestedAt":"2026-08-25T19:31:03.091Z","slug":"CVE-2026-45019","body":"## Overview\n\nChainlit 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.\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.\n\n## Package advisory (CVE-2026-45019)\n\nAffected packages:\n\n- `chainlit >= 2.4.0rc0, <= 2.11.1`\n\nPatched in:\n\n- `chainlit 2.12.0`\n\nSource: https://github.com/advisories/GHSA-hvfh-5mj3-5f3j","depth":"twilight","depthScore":40,"depthScoreParts":{"impact":39.6,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}