EUVD-2026-65737
GHSA-w3fx-mc44-mf6j
Severity by source
AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
The /mcp endpoint is unauthenticated and network-reachable with a low-complexity payload yielding full host RCE; the non-default MCP-enabled requirement is not a CVSS 3.1 base metric, so it does not lower PR or AC.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
4DescriptionCVE.org
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 stdio transport, the endpoint accepts a user-controlled fullCommand string. The validate_mcp_command() function in backend/chainlit/mcp.py checks only the executable name against config.features.mcp.stdio.allowed_executables and passes unchecked arguments to StdioServerParameters in backend/chainlit/server.py. Because npx supports the -c argument, an attacker can execute arbitrary shell commands with the privileges of the Chainlit process. If allowed_executables is unset, its None default is treated as allowing every executable. This issue is fixed in version 2.12.0.
Articles & Coverage 1
AnalysisAI
Unauthenticated remote code execution in Chainlit (2.4.0rc0 through 2.11.x) occurs when features.mcp.enabled is set to true, exposing the POST /mcp endpoint that accepts a user-controlled stdio command string. Because the allowlist only validates the executable name and passes arguments unchecked, an attacker can supply 'npx -y -c <payload>' to run arbitrary shell commands as the Chainlit process. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Requires features.mcp.enabled = true in .chainlit/config.toml - this is NOT the default (MCP has been disabled by default since v2.7.0), so vulnerable instances are those where an operator explicitly turned MCP on. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | This is a genuine top-priority issue for any deployment that meets the trigger condition, not merely a high-CVSS paper risk. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Vendor-released patch: 2.12.0 (2026-08-25) - upgrade to 2.12.0, but note this is a breaking change: legacy MCP config keys ([features.mcp.stdio], allowed_executables, [features.mcp.sse], [features.mcp.streamable-http]) now abort startup, client-supplied fullCommand is rejected, stdio servers must be declared server-side under [[features.mcp.servers]] with type = "stdio", and @chainlit/react-client 0.5.0 changes the connection API, so follow the MCP config and react-client migration guides in the changelog before upgrading. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory all Chainlit deployments and confirm whether features.mcp.enabled is set to true in production environments. …
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External POC / Exploit Code
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