Is CVE-2026-120492 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-120492 being exploited in the wild.

How severe is CVE-2026-120492?

Medium severity, with a CVSS score of 5.4, published 2 November 2026.

Is there a fix for CVE-2026-120492?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-120492 attacked?

It is attacked over the network, in a software library.

Am I affected by CVE-2026-120492?

Check whether you run Chainlit at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-120492: Chainlit MCP path validation bypass via semicolon

CVE-2026-120492 · Severity: medium · CVSS 5.4 · Published 2026-11-02

Chainlit is an open-source framework for building AI chat applications. This vulnerability allows unauthenticated attackers to bypass access controls on Model Context Protocol (MCP) endpoints by crafting URLs with semicolon characters that are stripped by origin servers, enabling requests to restricted resources outside the operator's allowlist.

Technologies: Chainlit. Vendors: Chainlit.

Quick answers

Is CVE-2026-120492 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-120492 being exploited in the wild.
How severe is CVE-2026-120492?: Medium severity, with a CVSS score of 5.4, published 2 November 2026.
Which products and versions are affected?: Chainlit 2.12.0.
Is there a fix for CVE-2026-120492?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-120492 attacked?: It is attacked over the network, in a software library.
Am I affected by CVE-2026-120492?: Check whether you run Chainlit at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability exists in the validate_mcp_url function which fails to reject semicolon characters in URL paths. Attackers can submit requests containing '..;' path segments to the /mcp endpoint; when origins strip path parameters at the semicolon, the actual request reaches paths outside the configured allowed_urls allowlist. The issue affects path-scoped MCP configurations where operators restrict which URLs can be accessed.

Affected products

Chainlit Chainlit 2.12.0

Timeline

2026-11-02: disclosed

References

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