---
title: "CVE-2026-45018: Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution"
url: https://erroneo.us/security/cve/CVE-2026-45018/
description: "CVE-2026-45018 (chainlit (PyPI)): Chainlit is a Python framework for building production-ready conversational AI applications. From 2.4.0rc0 until 2.12.0…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-08-25
date_modified: 2026-08-25
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-45018"
kev: false
cvss: 9.8
epss: 0.01086
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-45018: Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.1% , percentile 65: FIRST’s model estimates a 1.1% chance of exploitation activity in the next 30 days, higher than 65% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes chainlit (PyPI) >= 2.4.0rc0, <= 2.11.1, fixed in 2.12.0 . Check your lockfile, including transitive dependencies.

## What it is

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 validatemcpcommand() function in backend/chainlit/mcp.py checks only the executable name against config.features.mcp.stdio.allowedexecutables 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 allowedexecutables is unset, its None default is treated as allowing every executable. This issue is fixed in version 2.12.0.

## Affected packages

- PyPI `chainlit` >= 2.4.0rc0, <= 2.11.1 → fixed: 2.12.0

## Affected products (CVE record)

- Chainlit chainlit: >= 2.4.0rc0, < 2.12.0

## Severity

- GitHub_M CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-10-21): 1.09% probability of exploitation activity in the next 30 days; percentile 65.

## Sources

- [GitHub Advisory GHSA-w3fx-mc44-mf6j](https://github.com/advisories/GHSA-w3fx-mc44-mf6j)
- [CVE.org record CVE-2026-45018](https://www.cve.org/CVERecord?id=CVE-2026-45018)
- [NVD entry CVE-2026-45018](https://nvd.nist.gov/vuln/detail/CVE-2026-45018)
- [github.com](https://github.com/Chainlit/chainlit/security/advisories/GHSA-w3fx-mc44-mf6j)
- [github.com](https://github.com/Chainlit/chainlit/commit/0565fd0eccb915fce159929598b053ed79f6e0c9)
- [github.com](https://github.com/Chainlit/chainlit/blob/2.12.0/docs/security-advisory-2026-mcp.md#spl-2026-001--command-injection-via-mcp-stdio)
- [github.com](https://github.com/Chainlit/chainlit/releases/tag/2.12.0)

---
Source page: https://erroneo.us/security/cve/CVE-2026-45018/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt