Summary
Chainlit has command injection via MCP stdio transport that allows unauthenticated remote code execution
Impact
Critical. An unauthenticated remote attacker can execute arbitrary OS commands on the server with the privileges of the Chainlit process. This can lead to full host compromise, data exfiltration, lateral movement, and installation of persistent backdoors. Any Chainlit deployment with MCP enabled is affected.
Untrusted input reaches a shell command, allowing arbitrary commands to run on the host. Typical impact: code execution in the application's environment.
CVE-2026-45018 has a CVSS score of 9.8 (Critical). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.12.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Chainlit 2.12.0 removes fullCommand from the client request entirely. stdio MCP servers are now declared by the developer in .chainlit/config.toml under [[features.mcp.servers]] and selected by name at connection time; the command string never crosses the trust boundary from client to server, so there is no command left to sanitize and no allowed_executables mechanism anymore. Per-server environment variables are configured via an env mapping on the server entry rather than supplied by the client.
Frequently Asked Questions
- What is CVE-2026-45018? CVE-2026-45018 is a critical-severity OS command injection vulnerability in chainlit (pip), affecting versions >= 2.4.0rc0, <= 2.11.1. It is fixed in 2.12.0. Untrusted input reaches a shell command, allowing arbitrary commands to run on the host.
- How severe is CVE-2026-45018? CVE-2026-45018 has a CVSS score of 9.8 (Critical). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of chainlit are affected by CVE-2026-45018? chainlit (pip) versions >= 2.4.0rc0, <= 2.11.1 is affected.
- Is there a fix for CVE-2026-45018? Yes. CVE-2026-45018 is fixed in 2.12.0. Upgrade to this version or later.
- Is CVE-2026-45018 exploitable, and should I be worried? Whether CVE-2026-45018 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-45018 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-45018? Upgrade
chainlitto 2.12.0 or later.