Chainlit: Command injection via MCP stdio transport allows unauthenticated remote code execution

MITRE NVD CVE.ORG JSON API

Summary

CVECVE-2026-45018
StatePUBLISHED
AssignerGitHub_M
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-08-25 20:16:55 UTC
Updated2026-09-09 21:07:31 UTC
DescriptionChainlit 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.

Risk And Classification

Primary CVSS: v3.1 9.8 CRITICAL from [email protected]

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS: 0.006530000 probability, percentile 0.492030000 (date 2026-09-10)

Problem Types: CWE-78 | CWE-78 CWE-78: Improper Neutralization of Special Elements used in an OS Command ('OS Command Injection')

VersionSourceTypeScoreSeverityVector
3.1[email protected]Secondary9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
3.1CNADECLARED9.8CRITICALCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS v3.1 Breakdown

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Chainlit Chainlit affected >= 2.4.0rc0, < 2.12.0 Not specified

References

ReferenceSourceLinkTags
github.com/Chainlit/chainlit/releases/tag/2.12.0 [email protected] github.com
github.com/Chainlit/chainlit/blob/2.12.0/docs/security-advisory-2026-mcp.md [email protected] github.com
github.com/Chainlit/chainlit/security/advisories/GHSA-w3fx-mc44-mf6j 134c704f-9b21-4f2e-91b3-4a467353bcc0 github.com
github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6... [email protected] github.com
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