CVE-2026-45018
Chainlit: Command injection via MCP stdio transport allows unauthenticated remote code execution
- State
- Published
- Severity
- 9.8 Critical
- Published
- Aug 25, 2026
- Updated
- Aug 25, 2026
- Reserved
- May 8, 2026
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 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.
Scores
| CVSS | Score | Vector | Source |
|---|---|---|---|
| 3.1 | 9.8 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H | GitHub_M |
Weaknesses
- CWE-78 Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')
Affected Products
| Product | Versions |
|---|---|
chainlitChainlit |
|
References
- https://github.com/Chainlit/chainlit/security/advisories/GHSA-w3fx-mc44-mf6j
- https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9
- https://github.com/Chainlit/chainlit/blob/2.12.0/docs/security-advisory-2026-mcp.md#spl-2026-001--command-injection-via-mcp-stdio
- https://github.com/Chainlit/chainlit/releases/tag/2.12.0
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