CVE-2026-45019 Chainlit: SSRF via MCP SSE and streamable-http transports allows unauthenticated internal network access
Unauthenticated attackers can trigger Server-Side Request Forgery in Chainlit when MCP is enabled, accessing internal networks and metadata endpoints.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45019?
CVE-2026-45019 is a high-severity server-side request forgery vulnerability in chainlit, published on 25 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Weakness: CWE-918
Which versions are affected by CVE-2026-45019?
3 open source packages ship an affected version, including chainlit.
| Package | Affected | Fixed in |
|---|---|---|
chainlit PyPI | From 2.4.0rc0 | 2.12.0 |
chainlit PyPI | From 2.4.0rc0 | 2.12.0 |
chainlit PyPI | From 2.4.0rc0 | 2.12.0 |
How do I fix CVE-2026-45019?
Upgrade chainlit to 2.12.0 or later.
Upgrade, and send outbound requests through an allow-list that blocks internal addresses. More about Server-side request forgery.
Is CVE-2026-45019 being exploited?
There is no known exploitation of CVE-2026-45019 in the wild and no public exploit code.
Sources
Also known as GHSA-hvfh-5mj3-5f3j, PYSEC-2026-3811.