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Critical, CVSS 9.8amended

Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution

CVE-2026-45018GHSA-w3fx-mc44-mf6j

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (chainlit 2.12.0), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

  • PyPI chainlit

    Affected
    >= 2.4.0rc0, <= 2.11.1
    Fixed in
    2.12.0

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
9.8 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
EPSS
  • CVE-2026-45018: 1.09% estimated exploitation activity in the next 30 days; percentile 65.33 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Am I affected? Only if your deployment sets features.mcp.enabled = true in .chainlit/config.toml. MCP has been disabled by default since v2.7.0, so most Chainlit deployments are not affected. No authentication is required: /mcp is reachable by any client that can open a session. Summary When MCP is enabled (features.mcp.enabled = true), the POST /mcp endpoint for stdio transport accepts a user-controlled fullCommand string. The validatemcpcommand() function checks the executable name against a configurable allowlist but does not inspect or restrict the arguments. An attacker can pass npx -y -c 'ARBITRARY COMMAND' to execute arbitrary shell commands on the server with the privileges of the Chainlit process. Affected / patched versions | | | |---|---| | CVE | CVE-2026-45018 | | Affected | =2.4.0rc0, <2.12.0 with features.mcp.enabled = true (introduced in PR #1977, the change that added MCP support) | | Patched | 2.12.0 (releasing 2026-08-25) | Details validatemcpcommand() in…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-w3fx-mc44-mf6j

  2. Revision 2 · amended ·

    Amended from osv record GHSA-w3fx-mc44-mf6j

  3. Revision 1 · created ·

    Published from ghsa record GHSA-w3fx-mc44-mf6j

Agent brief

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# Patch Next advisory brief: CVE-2026-45018

Advisory: Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution
IDs: CVE-2026-45018, GHSA-w3fx-mc44-mf6j
Record: https://patchnext.com/advisories/cve-2026-45018 (revision 3, source checked 26 Oct 2026, 13:50 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Critical (CVSS 9.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: chainlit 2.12.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI chainlit: affected >= 2.4.0rc0, <= 2.11.1; fixed in 2.12.0

## Suggested inspection (read-only)
- `python -m pip show chainlit`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on chainlit.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-w3fx-mc44-mf6j (GitHub-reviewed advisory GHSA-w3fx-mc44-mf6j lists affected ranges: PyPI chainlit >=2.4.0rc0 <=2.11.1)
- Verified: https://osv.dev/vulnerability/GHSA-w3fx-mc44-mf6j (OSV record GHSA-w3fx-mc44-mf6j lists affected ranges: PyPI chainlit >=2.4.0rc0 <2.12.0 (fixed))

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